Convert between milligrams, grams, kilograms, metric tons, ounces, pounds, stones, and more.
1 Kilogram = 2.2046 Pound
A weight converter translates mass measurements between metric units (milligrams, grams, kilograms, metric tonnes) and imperial/US customary units (ounces, pounds, stones, short tons, long tons), plus specialised units like carats for gemstones and grains for ammunition and pharmacy. Weight conversion is needed daily in medicine, nutrition, logistics, commerce, sport, and engineering — wherever the metric and imperial worlds intersect.
An important distinction: technically, kilograms measure mass (the amount of matter), while the newton measures weight (the gravitational force on that mass). In everyday usage, the terms are used interchangeably — and this converter reflects that practical convention. All conversions use grams as the base unit, with every factor traceable to international definitions.
Before the metric system was established in France during the 1790s, weight measurement was a patchwork of local and commodity-specific standards that made international trade enormously complicated. The pound alone had multiple competing definitions: the tower pound (349.9 g) was used by the English Mint for silver weighing; the troy pound (373.2 g) governed gold, precious stones, and apothecary goods; the avoirdupois pound (453.6 g) applied to ordinary goods and bulk commodities; and the merchant pound (437.5 g) was used in certain trading contexts. A shipment of wool crossing from England to Flanders could be weighed by one standard at departure and a different one at arrival, creating systematic discrepancies that required specialist knowledge to resolve.
The metric system, introduced formally with the Metre Convention of 1875 and the creation of the Bureau International des Poids et Mesures (BIPM), resolved this chaos by establishing a single decimal-based hierarchy anchored to physical constants. Today, the kilogram is the internationally agreed base unit of mass, defined since 2019 via the Planck constant rather than a physical artefact. This universality — combined with the simplicity of base-10 scaling — is why the metric system now dominates every scientific, medical, and commercial domain globally, even in countries that continue using imperial units in everyday life.
Despite metric dominance in science and commerce, imperial units remain deeply embedded in everyday life in the United States and, to a lesser extent, the United Kingdom and Canada. This dual reality — metric for professional work, imperial for everyday conversation — means that weight conversion is not an edge case for travellers or scientists, but a routine daily task for millions of people checking their bathroom scales (pounds in the US, stones and pounds in the UK, kilograms in Australia), reading drug labels (mg and mcg), ordering goods from abroad, or following recipes from foreign cookbooks. This converter is designed to bridge that gap quickly, accurately, and without ambiguity.
All conversions route through grams as the base unit — the standard in SI's gram-kilogram hierarchy and the point at which international definitions anchor all imperial mass units. Every input is converted to grams, then to the target unit. This ensures consistent precision regardless of which pair of units is selected.
Rounding deserves special attention. All 10 unit conversion factors used in this calculator are either exact by international definition or derived from exact definitions. This means intermediate rounding — if applied too early — can compound errors. For example, if you round 1 kg to 2.205 lbs (instead of 2.20462 lbs) and then convert back to grams, you get 999.77 g instead of 1,000 g — a 0.023% error that accumulates through chained conversions. This calculator applies rounding only to the final displayed result, preserving full precision throughout the calculation chain.
Temperature affects weighing equipment but not the weight of the object itself (mass is temperature-independent). Precision balances specify a working temperature range (typically 10–30°C) because the electronic components, spring mechanisms, or load cells may drift outside that range. The mass of the item being weighed, however, is invariant with temperature — a 1 kg weight certified at 20°C remains 1 kg at 35°C, though its dimensions change slightly due to thermal expansion.
The following reference table shows the most commonly converted quantities across the three main weight systems. These figures are exact to the number of decimal places shown and are derived from the internationally defined conversion factors above.
Step 1: Convert stone to grams: 12.5 stone × 6,350.29318 g/stone = 79,378.66 g
Step 2: Convert grams to kg: 79,378.66 g ÷ 1,000 g/kg = 79.38 kg
Cross-check: 12.5 st × 14 lb/st = 175 lbs × 0.453592 = 79.38 kg ✓
The same two-step method works for any pair of units. To convert 3.5 troy ounces of silver to grams: Step 1 — 3.5 troy oz × 31.1034768 g/troy oz = 108.862 g. Step 2 — no further conversion needed since grams is the target. To then convert to kilograms: 108.862 g ÷ 1,000 = 0.108862 kg. Each step uses only multiplication or division by a known constant, making the chain auditable and reversible at any point.
Context: A seller shipping from the US must declare package weight in grams on the customs form CN22 (required for international postal shipments). Their scale reads 5.5 lbs.
Step 1: Convert pounds to grams: 5.5 lb × 453.59237 g/lb = 2,494.76 g
Step 2: Round to nearest gram for the customs declaration: 2,495 g
Step 3: Optionally express in kg for the carrier manifest: 2,494.76 g ÷ 1,000 = 2.495 kg
Why metric? The Universal Postal Union (UPU) mandates metric units on all international postal declarations. Customs duties are assessed per kg in most countries. Listing pounds or ounces on a CN22 form can cause delays or rejection at the destination country's customs office.
Weight conversion errors carry real consequences. In 1983, Air Canada Flight 143 (the 'Gimli Glider') ran out of fuel at 41,000 feet because ground crew calculated the required fuel mass in pounds rather than kilograms — loading 22,300 lbs instead of 22,300 kg, a shortfall of roughly 20,000 kg of fuel. The aircraft deadsticked to an emergency landing at an abandoned airstrip. No fatalities, but the cause was a single unit conversion error under time pressure.
In medicine, weight-based drug dosing (mg per kg of body weight) requires accurate conversion between the patient's recorded weight (often in lbs in the US) and the kg used in dosing tables. In commodity trading, mistaking a short ton for a metric tonne on a 10,000-unit contract introduces a 9.7% quantity error. Reliable weight conversion is a professional competency, not just a convenience.
Pharmaceutical dosing relies on weight conversion in ways that directly affect patient safety. Standard drug dosing protocols express doses in mg/kg — milligrams of drug per kilogram of body weight. A patient who weighs 180 lbs must have their weight converted to 81.6 kg before the prescribing physician can calculate the correct dose of, say, an antibiotic (e.g., amoxicillin at 25 mg/kg/day = 2,041 mg/day, rounded to 2,000 mg). Paediatric dosing is even more sensitive: a 22 lb toddler weighs exactly 10 kg, and a 10% conversion error translates directly into a potentially dangerous 10% overdose or underdose of a weight-adjusted medication.
International food labelling also illustrates why weight units matter across borders. A US nutrition label expresses serving sizes in grams and ounces and lists daily values in grams (macronutrients) and milligrams or micrograms (micronutrients). A UK label uses grams throughout. An Australian label follows metric with mandatory per-100 g columns. A consumer comparing the sodium content of two breakfast cereals — one bought in New York and one bought in London — must confirm they are both reading per-100 g figures, not per-serving, and that both serving sizes are expressed in the same unit. Weight literacy is a genuine nutritional literacy skill.
225 lbs × 0.45359237 = 102.06 kg. A common gym milestone ('two plates per side' = 4 × 20 kg + 20 kg bar = 100 kg in metric gyms, or 4 × 45 lbs + 45 lb bar = 225 lbs in US gyms). The slight discrepancy (102 kg vs 100 kg) explains why hitting '225' in the US doesn't perfectly translate to '100 kg' — you're 2 kg over. International athletes track both figures.
500 g of all-purpose flour ÷ 28.3495 = 17.64 oz. In cups: most references use ~120–130 g per cup for unsifted flour, so 500 g ÷ 125 g/cup = approximately 4 cups. Weight-based recipes (grams) are more reliable because ingredient density varies — 1 cup of packed brown sugar (200 g) is twice as dense as 1 cup of sifted powdered sugar (100 g). Using a kitchen scale eliminates volume measurement error entirely.
5 US short tons × 907.185 kg/short ton = 4,535.9 kg ≈ 4.536 metric tonnes. A freight invoice might show 5 ST (short tons) while the shipping line charges in metric tonnes. The 9.7% difference between a short ton (907 kg) and a metric tonne (1,000 kg) means 5 short tons of steel is significantly less than 5 metric tonnes — worth verifying before signing a purchase contract priced per tonne.
The seven mistakes below are drawn from documented incidents in aviation, medicine, commerce, and laboratory science — domains where weight conversion errors have caused accidents, financial losses, or patient harm. Understanding these failure modes helps build the habit of always stating units explicitly, verifying unit consistency before calculation, and cross-checking results against physical intuition.
Confusing avoirdupois ounces with troy ounces
The gold price is quoted per troy ounce (31.1035 g), but when people say 'ounce' in everyday life, they mean avoirdupois (28.3495 g) — 9.7% lighter. Buying 1 troy oz of gold and thinking you're getting 1 avoirdupois oz of weight in another metal leads to miscalculation. When reading precious metals prices, always assume troy ounces. When measuring food or body care products, always assume avoirdupois ounces.
Mixing up metric tonnes, short tons, and long tons
All three are called 'ton' in everyday speech but differ significantly. A metric tonne (1,000 kg) is 10.2% heavier than a US short ton (907 kg) and 1.6% lighter than a UK long ton (1,016 kg). In commodity markets (oil, steel, grain), prices are always in metric tonnes internationally. US domestic markets may use short tons. Applying the wrong conversion to a 10,000-tonne order introduces errors worth tens of thousands of dollars.
Confusing milligrams and micrograms in medicine
1 mg = 1,000 μg. Medication doses are sometimes written ambiguously: 'mcg' (microgram) and 'mg' (milligram) look similar in handwriting and some fonts. A dose of 0.5 mg mistakenly read as 0.5 mcg results in a 1,000-fold underdose; 500 mcg read as 500 mg gives a 1,000-fold overdose. Medical organisations recommend never abbreviating micrograms as 'μg' on handwritten prescriptions — spell out 'microgram' in full to prevent errors.
Using net weight when gross weight is needed (or vice versa)
A 500 g jar of peanut butter has a net weight of 500 g (the peanut butter) but a gross weight of roughly 650 g (including glass jar and lid). For freight costing, shippers need gross weight. For recipe scaling, you need net weight. Customs declarations require both. A delivery driver estimating load weight from product labels (which show net weight) may significantly underestimate vehicle load, risking overloading.
Assuming 1 litre of liquid = 1 kg for non-water liquids
1 litre of water ≈ 1 kg is a useful approximation, but other liquids vary significantly: 1 L of milk ≈ 1.03 kg; 1 L of vegetable oil ≈ 0.92 kg; 1 L of honey ≈ 1.41 kg; 1 L of mercury = 13.55 kg. Using the 1 L = 1 kg rule for honey or oil introduces 40% and 8% errors respectively — significant for food production, chemical batch calculations, and custom tank weight estimates.
Ignoring buoyancy in precision weighing
Air exerts a buoyant force on any object — approximately 1.2 kg per cubic meter displaced. For everyday weighing, this is negligible. But for precision analytical work weighing large-volume, low-density objects (expanded polystyrene, gas-filled vessels), buoyancy corrections matter. A 1 m³ block of expanded polystyrene nominally weighing 15 kg in vacuum could show a reading 1.2 kg lighter in air due to buoyancy — an 8% error. Precision balances in calibration laboratories use buoyancy-corrected values.
Confusing weight (force) and mass in engineering formulas
In Newton's second law (F = ma), force is in Newtons, mass in kilograms, acceleration in m/s². When US engineers use pounds-force (lbf) and pounds-mass (lbm) in the same equation without a conversion factor (gc = 32.174 lbm·ft/lbf·s²), the units don't balance and the calculated force is wrong by a factor of 32.174. This class of error contributed to the Gimli Glider fuel miscalculation (1983 Air Canada 767) and the Mars Orbiter loss (1999). Always use SI or apply the gc conversion factor consistently in US customary calculations.
In physics, mass (kg) and weight (N = kg·m/s²) are distinct. Standard gravity is defined as exactly 9.80665 m/s² — so 1 kg mass has a weight of 9.80665 N at standard gravity. Scales actually measure force and display an inferred mass assuming standard gravity. A calibrated scale in Denver (altitude 1,609 m, g ≈ 9.796 m/s²) reads slightly high compared to one at sea level. For precision metrology, a Kibble balance is used to measure mass via electromagnetic force and the Planck constant, bypassing gravitational uncertainty entirely.
The 2019 redefinition of the kilogram was a landmark in measurement science. For 130 years, the global mass standard was a physical artefact — IPK, a platinum-iridium cylinder in Sèvres — that could not be verified without comparing it to a copy, and copies drifted over decades. The new SI defines the kilogram through the fixed Planck constant (h = 6.62607015 × 10⁻³⁴ J·s), making mass measurement reproducible anywhere using a Kibble balance without reference to a physical object. All avoirdupois units (oz, lb, ton) remain anchored to this definition via the exact 1 lb = 453.59237 g relationship from 1959.
Several domains use their own weight systems. Jewellers use the troy system (troy oz, troy lb, grains) and metric carats. Pharmacists historically used the apothecary system (grains, scruples, drams, apothecary ounces) — now largely replaced by metric. Ammunition reloaders use grains for powder charges and bullet weight. The Beaufort scale for wind speed has no mass equivalent, but the Saffir-Simpson hurricane scale does involve wind-generated pressure measured in force per unit area. Knowing which weight system applies to a given domain prevents systematic misinterpretation of specifications.
The apothecary system deserves particular mention as a cautionary tale about unit system proliferation. Used in European pharmacy from the Middle Ages through the 19th century, it defined a hierarchy of units: 1 apothecary pound = 12 apothecary ounces = 96 drams = 288 scruples = 5,760 grains. The apothecary ounce (31.1035 g) happens to equal the troy ounce exactly — reflecting their common origin in medieval European trade. The US officially abandoned apothecary measures in pharmacy in 1971 (replaced by metric), but older formularies, some compounding references, and historical medical documents still use drams (3.888 g) and scruples (1.296 g). A pharmacist encountering a legacy prescription written in apothecary units needs to convert carefully to avoid dosing errors.
The precious metals and gemstone industries operate on entirely separate weight systems from everyday commerce, and confusing them carries significant financial consequences. Gold, silver, platinum, and palladium are all priced and traded in troy ounces. One troy ounce equals 31.1034768 grams — approximately 9.7% heavier than the avoirdupois ounce (28.3495 g) used for food and everyday goods. The troy system also defines the troy pound as 12 troy ounces (373.24 g), which is lighter than the avoirdupois pound of 16 oz (453.59 g). When a bullion dealer quotes "$1,900 per ounce" for gold, that is always per troy ounce — not the common ounce. Purchasing 10 "ounces" of gold while assuming avoirdupois units would mean receiving 10.97% more gold than expected by price, or alternatively, paying 10.97% above spot for the same quantity.
Diamonds and coloured gemstones are measured in metric carats, where 1 carat = exactly 0.2 grams = 200 milligrams. This is an internationally standardised definition (OIML, 1907) and is not to be confused with gold karat (also written 'carat' in British English), which measures purity on a scale of 0–24 and has nothing to do with mass. A 0.5 ct (half-carat) round brilliant diamond weighs exactly 0.1 grams. Diamond pricing per carat is non-linear — a 1.00 ct stone commands a disproportionately higher price per carat than two 0.50 ct stones of equal quality, because of the rarity premium on larger stones. This makes accurate carat weight measurement critical to valuation, typically verified to the nearest 0.01 ct (0.002 g) using a precision jeweller's scale.
The grain (gr) is another unit that persists in precious metals contexts: 1 troy ounce = 480 grains, while 1 avoirdupois ounce = 437.5 grains. At 64.79891 mg per grain, the grain is one of the smallest named US customary units of mass. In gold assaying and historical coinage, grain weights were used to specify coin standards — the US Silver Dollar of 1792 was defined as 416 grains of standard silver. Today, grains remain relevant in the bullion coin market for specifying the precise weight of fractional coins and in the analytical assay of precious metal concentrations in ore samples.
Body weight tracking sits at the intersection of the imperial and metric worlds more than almost any other everyday measurement. A fitness app used in the United States stores weight in pounds; the same app used in the UK may default to stones and pounds; in continental Europe, it uses kilograms. When a user switches phones, migrates accounts, or compares data with a training partner in a different country, unit conversions happen invisibly — or incorrectly if the software does not handle them properly.
Barbell training introduces its own weight literacy requirements. Commercial weight plates in the US are typically labelled in pounds (45 lb, 25 lb, 10 lb, 5 lb, 2.5 lb), while competition powerlifting and Olympic weightlifting use kilogram plates (20 kg, 15 kg, 10 kg, 5 kg, 2.5 kg, 1.25 kg, 0.5 kg). An athlete who trains in a US commercial gym with a 45 lb barbell and four 45 lb plates is lifting 45 + (4 × 45) = 225 lbs = 102.06 kg — not a round number in metric. International competition plates use a 20 kg bar (44.09 lbs) as standard, so the weight loaded differs from US gym setups even when the plate count is identical.
Boxing, wrestling, and combat sports use weight classes defined in both kilograms (official WBC/WBA/IBF standards) and pounds (commonly reported in US media). A boxer who competes at super featherweight (130 lbs = 58.97 kg) needs to cut weight precisely to make the limit. A 1 lb difference (0.45 kg) can be the difference between making or missing weight at the official weigh-in. Professional fighters and their trainers track weight in both systems simultaneously and use this converter equivalents daily during camp.
Endurance sports such as marathon running, cycling, and triathlon add another layer: power-to-weight ratio (watts per kilogram, W/kg) is the primary performance metric for competitive cyclists climbing hills. A rider who produces 350 watts at 70 kg has a W/kg of 5.0 — world-class threshold is around 6.0–6.5 W/kg for grand tour climbers. Because this ratio uses kilograms in the denominator, US-based cyclists who track weight in pounds must convert accurately: 155 lbs ÷ 2.20462 = 70.31 kg, not 70 kg — a 0.44% difference that matters when comparing to published benchmarks. Race weight targets, equipment weight limits (UCI rules cap road bike weight at 6.8 kg = 14.99 lbs), and even aerodynamic drag calculations all require weight unit fluency.
Food labelling regulations add another dimension to weight literacy for the home cook. In the European Union, pre-packaged foods must display the net quantity in metric units (grams, kilograms, millilitres, or litres) under Regulation (EU) No 1169/2011. In the United States, the Fair Packaging and Labeling Act requires both metric and US customary units on most consumer packages — so a jar shows both "NET WT 16 OZ (454 g)". This dual labelling is why US consumers encounter grams on food packages even though they may cook with cups and ounces. Understanding the relationship helps when following international recipes or comparing nutritional data across products from different markets.
Professional kitchens and bakeries have largely shifted to gram-based recipes because weight measurement eliminates the variability inherent in volume cups and spoons. Bread baking is particularly sensitive: a bread formula calling for 1,000 g flour, 680 g water (68% hydration), 20 g salt, and 10 g instant yeast produces a consistent result regardless of altitude, humidity, or the baker's cup-scooping technique. Converting this to US volume measures introduces unnecessary error — flour alone can range from 120 g to 150 g per cup depending on sifting, packing, and the specific flour variety.
Nutritional science uses weight as the foundation for all dietary reference values. The Dietary Reference Intakes (DRIs) published by the US National Academies express requirements in grams per day (macronutrients), milligrams per day (minerals, some vitamins), and micrograms per day (trace elements, fat-soluble vitamins). Comparing nutritional content across products therefore requires consistent unit understanding: a product label showing 3.5 g sodium per 100 g versus one showing 3,500 mg per 100 g are identical — but the units look very different at a glance. Similarly, omega-3 recommendations (1–2 g EPA+DHA/day) must be compared against fish oil capsule labels that may show mg per capsule.
Structural engineers, civil engineers, and architects work with weight at scales ranging from individual fasteners (grams) to bridge loads (thousands of metric tonnes). A structural specification might list the self-weight of a concrete floor as 25 kN/m³ (kilonewtons per cubic metre) — this is a weight density, derived from the mass density of 2,500 kg/m³ multiplied by standard gravity (9.80665 m/s²). Converting between mass, weight force, and pressure units is routine structural work. Crane lift plans specify both the gross load in metric tonnes and the equivalent in kilonewtons for the rigging calculations.
In geotechnical engineering, soil bearing capacity is often expressed in kPa (kilopascals = kN/m²) or in the older unit of tons per square foot (tsf), which could be metric or short tons depending on the country of origin of the report. A foundation designed for 2 tsf bearing pressure in an old US report differs from one designed for 2 metric t/m² — confusing the two could result in a foundation that is undersized by a factor related to the foot-to-metre conversion squared. Careful unit tracking is a professional obligation, not merely good practice, in structural and geotechnical work.
Highway and road construction provides a daily example of large-scale weight management. A standard semi-trailer truck in the US has a gross vehicle weight rating (GVWR) of 80,000 lbs (36,287 kg). European limits are typically 40–44 metric tonnes (88,185–97,003 lbs) depending on the number of axles. A shipment dimensioned for US road transport may legally exceed EU weight limits by more than 10%, or vice versa — making weight unit conversion a critical step in cross-border logistics planning, not just paperwork.
The table below provides at-a-glance reference values for the most frequently needed weight conversions. All figures are rounded to 4 significant figures for practical use. For exact values, use the converter above.
These everyday reference weights serve a second purpose beyond convenience: they let you sanity-check conversion results. If a calculation tells you that a loaf of bread weighs 7.5 kg, you know immediately something went wrong — either the input was in grams (680 g, not 680 kg) or a decimal point slipped. Building an intuitive sense of weight across unit systems is one of the most practical benefits of regularly working with weight conversions.
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Before performing any weight conversion or calculation that has real-world consequences — a medication dose, a shipping declaration, a structural load estimate, a commodity trade — run through this five-point checklist to avoid the most common unit errors.
Identify the unit system of every input
Write the unit symbol next to every number. "225" means nothing without "lbs" or "kg". If the source document does not specify, find out before proceeding — do not assume.
Verify which "ounce" and which "ton" is meant
Ounce: avoirdupois (28.35 g) or troy (31.10 g)? Ton: metric tonne (1,000 kg), short ton (907 kg), or long ton (1,016 kg)? These ambiguities cause the majority of real-world weight errors.
Distinguish net weight from gross weight
Product labels show net weight. Shipping documents need gross weight. Customs declarations require both. Confirm which is required before entering a number.
Cross-check the result against physical intuition
Does the answer make sense? A person weighing "700 kg" or a shipping container weighing "5 grams" are immediate red flags. Compare to known reference weights — an average person is 70 kg; a car is 1,200–2,000 kg.
Reverse-convert to verify
Take the output and convert it back to the original unit. It should match the starting value to within rounding. A mismatch indicates a wrong conversion factor or a decimal error.
While the converter handles exact calculations, knowing a few mental arithmetic shortcuts lets you estimate weight conversions in seconds without pulling out a device. These approximations are accurate enough for everyday purposes and can help you quickly sense-check a calculated result.
The key insight behind all these shortcuts is that conversion factors cluster near simple fractions or multiples: 2.20462 is close to 2.2 (= 11/5); 0.45359 is close to 0.45 (= 9/20); 28.3495 is close to 28 (= 4 × 7). By memorising just two or three anchor facts — 1 kg ≈ 2.2 lbs; 1 oz ≈ 28 g; 1 stone = 14 lbs — you can derive almost any everyday conversion by chaining these anchors together. For example, to convert 5 stone 10 lbs to kg without a calculator: 5 × 14 = 70 lbs + 10 lbs = 80 lbs ÷ 2.2 ≈ 36.4 kg (exact: 36.29 kg). The chain introduces less than 0.3% error.
Estimation skills are especially valuable when travelling internationally. A US traveller in Europe reading a road sign that says "Max Load 3.5 t" needs to instantly judge whether their rented campervan exceeds that limit. Knowing that 3.5 metric tonnes ≈ 3.5 × 2,200 = 7,700 lbs ≈ 3.85 short tons gives an immediate answer. Similarly, a European traveller in the US seeing a product labelled "5 lbs" can quickly estimate 5 ÷ 2.2 ≈ 2.3 kg. These quick estimates prevent misunderstandings without requiring a phone or calculator.
kg to lbs: multiply by 2.2 (or double and add 10%)
Example: 80 kg × 2.2 = 176 lbs (exact: 176.37 lbs). Alternatively: 80 × 2 = 160, plus 10% (16) = 176. Error: 0.2%. Reliable for body weight, luggage, and food quantities up to a few hundred kg.
lbs to kg: divide by 2.2 (or halve and subtract 10%)
Example: 150 lbs ÷ 2.2 = 68.2 kg (exact: 68.04 kg). Alternatively: 150 ÷ 2 = 75, minus 10% (7.5) = 67.5 kg. The division method is slightly more accurate (0.2% error vs 0.7% for the halve-minus-10% method).
grams to ounces: divide by 28 (or multiply by 0.035)
Example: 250 g ÷ 28 = 8.93 oz (exact: 8.818 oz). The division by 28 introduces a 1.25% overestimate — acceptable for kitchen use. For tighter accuracy, divide by 28.35.
ounces to grams: multiply by 28 (or 30 for rough estimates)
Example: 6 oz × 28 = 168 g (exact: 170.1 g). Multiplying by 30 gives 180 g — a 5.8% overestimate, fine for rough checks but not for recipe scaling. Use × 28 for kitchen accuracy and × 28.35 for precise conversions.
stone to kg: multiply by 6.35
Example: 11 stone × 6.35 = 69.85 kg (exact: 69.85 kg — this approximation is exact to 4 significant figures). For stone-and-pounds: convert pounds to a decimal fraction of a stone first (e.g., 11 st 7 lbs = 11.5 st × 6.35 = 73.0 kg; exact: 73.03 kg).
metric tonnes to short tons: add 10%
Example: 500 metric tonnes → add 10% (50) → ≈ 550 short tons (exact: 551.16 short tons). Error: 0.2%. Conversely, short tons to metric tonnes: subtract about 9% (500 short tons × 0.91 ≈ 455 t; exact: 453.6 t).
Multiply kilograms by 2.20462 to get pounds. For example, 70 kg × 2.20462 = 154.32 lbs. The exact conversion factor is 1 kg = 2.2046226218... lbs, derived from the international definition that 1 pound = exactly 453.59237 grams. Quick mental estimate: multiply kg by 2.2 (introduces 0.2% error). To convert pounds to kilograms, multiply by 0.45359237 or divide by 2.20462.
There are exactly 1,000 grams in one kilogram. The SI prefix 'kilo-' means one thousand (10³). This relationship is exact by definition: 1 kg = 1,000 g = 1,000,000 mg. Converting within the metric system only requires moving the decimal: 2.5 kg = 2,500 g = 2,500,000 mg. This regularity is why the metric system dominates medicine, chemistry, and food labelling worldwide — no memorization of irregular ratios required.
Mass is the amount of matter in an object, measured in kilograms or pounds-mass, and is the same everywhere in the universe. Weight is the gravitational force on that mass, measured in Newtons (F = mg), and changes with gravitational field strength. On the Moon (g ≈ 1.62 m/s²), a 70 kg person weighs about 113 N — compared to 686 N on Earth — but their mass remains 70 kg. In everyday language, 'weight' and 'mass' are used interchangeably (both expressed in kg or lbs), though physicists distinguish them precisely.
Multiply avoirdupois ounces by 28.349523125 to get grams (this is an exact definition: 1 lb = 453.59237 g; 1 oz = 453.59237/16 g). For quick estimates, multiply ounces by 28.35. Examples: 8 oz × 28.35 = 226.8 g; a standard stick of butter (4 oz) ≈ 113.4 g. Note: the troy ounce (used for precious metals) is heavier — 1 troy oz = 31.1034768 g. Always specify which ounce is meant in financial or metals contexts.
A stone is a unit of weight used primarily in the UK and Ireland, equal to exactly 14 pounds = 6.35029 kg. Body weight in the UK is commonly expressed as stones and pounds: '11 stone 5' means (11 × 14) + 5 = 159 lbs = 72.1 kg. To convert kilograms to stone, divide by 6.35029. Medical forms and bathroom scales in the UK often show kg, stone, and lbs simultaneously. The stone has no official standing in SI but remains entrenched in British everyday usage.
A metric ton (tonne, t) = 1,000 kg = 2,204.623 lbs. A short ton (US ton) = 2,000 lbs = 907.185 kg — about 91% of a metric ton. A long ton (UK ton) = 2,240 lbs = 1,016.047 kg — about 101.6% of a metric ton. Commodity prices (oil, grain, steel) are quoted internationally in metric tons. US domestic bulk freight often uses short tons. UK historical shipping records use long tons. Mixing these up causes significant financial errors in large-quantity trade — always verify which ton is used.
There are exactly 1,000 milligrams in one gram. The prefix 'milli-' means 10⁻³. So: 1 g = 1,000 mg; 1 mg = 0.001 g; 500 mg = 0.5 g. Milligrams are the standard unit for pharmaceutical dosing: a standard adult ibuprofen tablet is 200 mg or 400 mg; a daily vitamin D supplement may be 1,000–2,000 IU (about 25–50 μg). Dietary sodium on nutrition labels is given in mg — the recommended limit is 2,300 mg (2.3 g) per day.
One metric carat (ct, used for gemstones) = exactly 0.2 grams = 200 milligrams. A 1-carat diamond weighs 0.2 g. The metric carat has been internationally standardised since 1907. Important: gemstone carats (mass) are completely different from gold karats (purity). 24-karat gold means pure gold (999.9 fine); it is not a mass unit. A 1-carat diamond set in an 18-karat gold ring: the '1 ct' is the diamond's mass (0.2 g) and '18k' describes the gold alloy composition.
Multiply pounds by 0.45359237 to get kilograms (exact by definition: 1 lb = 453.59237 g). Quick mental estimate: divide pounds by 2.2. A 200 lb person weighs 200 × 0.45359237 = 90.72 kg. Reverse: 90.72 kg × 2.20462 = 200 lb. This conversion is needed daily for medical records, fitness apps, international airline luggage limits, and food portion sizing across countries with different unit systems.
The United States, Myanmar, and Liberia primarily use pounds for body weight and everyday mass. The United Kingdom uses both — kilograms officially in healthcare and kilograms/stones in everyday speech. Canada officially uses kilograms but many Canadians still use pounds colloquially. All other countries use kilograms as the primary unit. Scientific, medical, and laboratory contexts worldwide use kilograms exclusively. International drug dosing is calculated in mg/kg of body weight, making kilogram measurements standard in healthcare globally.
Divide grams by 28.349523125 to get avoirdupois ounces (or multiply by 0.03527396). For example, 250 g ÷ 28.3495 = 8.818 oz ≈ 8¾ oz. Common kitchen conversions: 100 g ≈ 3.53 oz; 250 g ≈ 8.82 oz; 500 g ≈ 17.64 oz; 1 kg ≈ 35.27 oz. US recipe books list quantities in cups and ounces; European recipes use grams. Weight measurements are more precise for baking — ingredient density varies, so 1 cup of flour can range from 120 to 150 g depending on how tightly packed.
Avoirdupois ounce (the common oz): 1 oz = 28.3495 g. Used for everyday goods — food, body weight, shipping. Troy ounce: 1 troy oz = 31.1034768 g — about 9.7% heavier. Used exclusively for precious metals (gold, silver, platinum, palladium) and gemstones in financial trading. There are 16 avoirdupois ounces in a pound but only 12 troy ounces in a troy pound. Gold spot prices ($X/troy oz) and silver prices always use troy ounces. Confusing the two when buying or selling bullion introduces a systematic ~10% pricing error.
One liter of pure water weighs almost exactly 1 kilogram at 4°C (the temperature of maximum density). This was the original intent of the metric system — to tie mass and volume together through water. At 20°C (room temperature), 1 L of water weighs 0.9982 kg — close enough that 1 L ≈ 1 kg is a reliable rule for water. This means: a 500 mL bottle of water weighs ≈ 0.5 kg (plus bottle); a 5-gallon (18.93 L) water jug weighs ≈ 18.93 kg (41.7 lbs).
The kilogram (kg) is the SI base unit for mass — one of the seven SI base units. Since May 2019 (the 'New SI'), the kilogram is defined by fixing the value of the Planck constant h = 6.62607015 × 10⁻³⁴ J·s exactly. This replaced the International Prototype of the Kilogram (IPK) — a platinum-iridium cylinder kept in a vault in Sèvres, France — which had been the global mass standard since 1889 but had subtly drifted from copies over time. The new definition makes the kilogram reproducible anywhere using a Kibble balance.
The most reliable mental shortcut: multiply kg by 2.2. Example: 75 kg × 2.2 = 165 lbs (exact: 165.35 lbs). Another method: double the kg and add 10% — 75 × 2 = 150, plus 10% (15) = 165. For reverse (lbs to kg): halve the pounds and subtract 10%. 150 lbs ÷ 2 = 75, minus 10% (7.5) = 67.5 kg (exact: 68.04 kg — slightly off, so the 'divide by 2.2' method is more accurate). The 2.2 approximation introduces only 0.2% error.
A microgram (μg or mcg) is one-millionth of a gram (10⁻⁶ g = 0.001 mg). It is the standard unit for trace minerals, vitamins, and hormone concentrations: vitamin D recommendations are 600–800 IU (15–20 μg); folate requirements are 400 μg/day; thyroid hormone T4 doses are 25–200 μg/day. Air quality standards measure PM2.5 in micrograms per cubic meter (μg/m³). Confusion between mg and μg in pharmacy is a 1,000-fold difference that has caused fatal medication errors — always verify units when reading medical prescriptions.
Multiply metric tonnes by 1.10231 to get short tons (US tons). For example, 500 t × 1.10231 = 551.16 short tons. To reverse, multiply short tons by 0.907185. Context matters enormously in bulk commodity trading: a 50,000-tonne cargo ship contract in metric vs. a 50,000 short-ton contract differs by 5,511 tons (≈ 5,000 metric tonnes) — worth millions of dollars in grain or coal. Always specify the ton type in international commercial contracts.
Common references: a standard AA battery ≈ 23 g; a smartphone ≈ 170–220 g; a 1-litre water bottle ≈ 1 kg; a standard house brick ≈ 2.0–2.7 kg (4.4–6 lbs); a bag of cement ≈ 25 kg (55 lbs) in EU / 94 lbs (42.6 kg) per sack in US; a car battery ≈ 15–25 kg (33–55 lbs); an average person ≈ 70 kg (154 lbs). These reference weights help calibrate unit conversions and verify whether a calculated result is physically plausible.
Weight (gravitational force) decreases slightly with altitude because gravity weakens with distance from Earth's centre. At sea level, g ≈ 9.807 m/s². At 10,000 m (airliner cruise altitude), g ≈ 9.776 m/s² — about 0.3% less. At the summit of Everest (8,849 m), g ≈ 9.773 m/s² — your scale weight would be about 0.35% less than at sea level. Mass, however, does not change. For weighbridge weighing at high altitudes, calibration must account for local g. Standard scales are calibrated for sea level gravity.
A grain (gr) = exactly 64.79891 mg = 0.0647989 g. It is one of the oldest units of mass, originally based on a grain of cereal (barley or wheat). Grains are still used in: firearms and ammunition (bullet weight in grains; 7,000 grains = 1 lb avoirdupois); pharmacy (some older prescriptions); archery (arrow weight). The conversion: 1 oz avoirdupois = 437.5 grains; 1 troy oz = 480 grains. Digital scales accurate to 0.001 g (1 mg) are needed for grain-level measurements in reloading.
Small quantities (milligrams to grams) require analytical balances with 4–6 decimal places of precision. Laboratory analytical balances measure to 0.0001 g (0.1 mg). Micro-balances measure to 0.000001 g (1 μg). For home reloading (gunpowder charges in grains), beam balances or precision digital scales accurate to ±0.1 gr (6.5 mg) are standard. In pharmacy, compounding balances accurate to ±5 mg are required by law for doses under 120 mg. Consumer kitchen scales accurate to ±1 g are insufficient for pharmaceutical or scientific work.
Net weight is the weight of the product alone, excluding all packaging. Gross weight includes the product plus all packaging (box, pallet, wrapping). Tare weight is the weight of the packaging alone; gross weight = net weight + tare weight. Food labels show net weight (e.g., '500 g' means the food content, not the container). In international shipping, freight charges may be based on gross weight or volumetric weight (whichever is greater). Customs declarations typically require both gross and net weight for tariff and VAT calculations.
Divide the total pounds by 14 — the whole number is the stone value, and the remainder is the pounds. Formula: stones = floor(lbs ÷ 14); remaining lbs = lbs mod 14. Example: 154 lbs ÷ 14 = 11 stone exactly (154 mod 14 = 0). Example: 163 lbs: 163 ÷ 14 = 11 stone remainder 9 — so 11 stone 9 lbs. To convert stone-pounds to kilograms: total lbs = (stones × 14) + lbs; then multiply by 0.453592.
A slug is the US customary unit of mass (not weight), defined as the mass that accelerates at 1 ft/s² under a force of 1 pound-force. 1 slug = 14.5939 kg = 32.174 lbs-mass. It appears in aerospace and structural engineering equations that use lb-force and ft/s² without converting to SI. In SI, the equivalent concept uses kilograms and Newtons (F = ma). The slug is rare outside US aerospace — most engineers use SI or switch to lb-force/lb-mass conventions.
Humidity affects precision weighing through two mechanisms. First, buoyancy: moist air is less dense than dry air (water vapour displaces heavier nitrogen/oxygen), so buoyant force decreases and a mass weighs fractionally more in dry air. For loads above 10 kg, the buoyancy correction is less than 0.015% — negligible for most uses. Second, hygroscopicity: materials like paper, food, and hygroscopic chemicals absorb moisture from humid air, gaining mass over time. Laboratories dry samples before weighing and use enclosed balances with desiccants to prevent moisture uptake.
SI uses prefixes to express any mass. The largest named SI unit of mass is the quettagram (Qg = 10³⁰ g), added in 2022 — useful for expressing the mass of galaxy clusters. The smallest is the quectogram (qg = 10⁻³⁰ g). The kilogram itself is the SI base unit; unusually, it already contains the prefix 'kilo-'. The electronvolt/c² (eV/c²) is used in particle physics for subatomic masses. A proton ≈ 938.3 MeV/c² = 1.6726 × 10⁻²⁷ kg. Common cooking range: milligrams (spices) to kilograms (meat, flour).
Since the 1959 International Yard and Pound Agreement, 1 pound is defined as exactly 453.59237 grams. This makes the pound a derived unit from the metric system — it is no longer defined by a physical artifact but by an exact mathematical relationship to the kilogram. Prior to 1959, the US and UK pound differed slightly (US = 453.59243 g; UK = 453.59237 g). The agreement harmonized them. This means all avoirdupois conversions (ounces, pounds, tons) now have exact metric equivalents with no rounding error in the conversion factors.
Freight is typically charged based on either actual weight or volumetric weight (dimensional weight), whichever is greater. Volumetric weight formula: volume (cm³) ÷ 5,000 = kg (for most couriers). A lightweight but large box might have a volumetric weight higher than its actual weight — you pay the higher figure. International air freight uses metric tons (1,000 kg); ocean freight uses metric tons or revenue tons. Domestic US trucking uses short tons. Always confirm whether weight limits in logistics contracts are metric tonnes, short tons, or long tons.
Key material densities per cubic meter: Water ≈ 1,000 kg (1 tonne); Concrete ≈ 2,300–2,500 kg (2.3–2.5 tonnes); Structural steel ≈ 7,850 kg (7.85 tonnes); Aluminium ≈ 2,700 kg; Oak wood ≈ 700–900 kg; Granite ≈ 2,600–2,800 kg. Knowing these densities allows weight estimation from volume: a 10 m³ reinforced concrete slab weighs approximately 23,000–25,000 kg (23–25 tonnes). This is essential for structural engineering load calculations and crane lift planning.
Yes — if you know a material's density (mass per unit volume, in kg/m³ or g/cm³), you can convert between weight and volume: Volume = Mass ÷ Density. For water: 5 kg ÷ 1,000 kg/m³ = 0.005 m³ = 5 liters. For steel: 100 kg ÷ 7,850 kg/m³ = 0.01274 m³. This calculation is essential for chemical mixing (need X grams of solute to make a Y% solution by volume), concrete mixing (cement bags to cubic meters), and hydroponics (nutrient solution preparation).
Conversion method: All weights convert through grams as the base unit using exact international definitions. Avoirdupois units per the 1959 International Yard and Pound Agreement (1 lb = 453.59237 g exactly). Troy ounce per the international definition (31.1034768 g exactly). Metric carat = 0.2 g exactly (OIML standard). SI kilogram per BIPM SI Brochure 9th edition (2019), defined via Planck constant.
Precision: Conversions are computed in JavaScript 64-bit floating-point arithmetic (IEEE 754 double precision), which provides approximately 15–17 significant decimal digits. For values within the range of everyday use (milligrams to metric tonnes), the floating-point rounding error is less than 1 part in 10¹⁰ — far below the precision of any physical weighing instrument. Results are displayed to a maximum of 6 significant figures to avoid conveying false precision.
Unit coverage: This converter includes the 10 most widely used weight units: milligram (mg), gram (g), kilogram (kg), metric tonne (t), ounce avoirdupois (oz), pound (lb), stone (st), short ton (US ton), long ton (UK ton), and metric carat (ct). Troy ounce conversions are noted in the FAQ section. Apothecary units (scruple, dram, apothecary ounce) and obscure historical units are not included; for those, consult NIST Handbook 44.
Data sources: NIST SP 811; BIPM SI Brochure (9th edition, 2019); OIML R 111 (weights for mass measurement); 1959 International Yard and Pound Agreement. Disclaimer: For pharmaceutical dosing, legal metrology, or engineering load calculations, use calibrated instruments and consult certified standards. Results are for informational purposes only. Last updated: June 2026. Maintained by Financial Growth Hub.
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