Convert milligrams, grams, kilograms, metric tons, ounces, pounds, and stone instantly — with every step shown. Free and exact.
Home » Unit Converters » Weight Converter
Whether you are following a recipe in grams, checking a luggage limit in kilograms, or reading your weight in pounds, mass measurements cross systems constantly. Our free Weight Converter translates instantly among milligrams, grams, kilograms, metric tons, ounces, pounds, and stone — using the exact international definitions — and shows the two-step working so the result is never a mystery.
A quick but important distinction: in everyday speech we say “weight,” but most converters (this one included) convert mass — the amount of matter in an object, measured in kilograms. True weight is a force (mass × gravity) measured in newtons. On Earth’s surface the two are proportional, which is why bathroom scales can display kilograms while technically measuring force. For cooking, shipping, fitness, and luggage, mass conversion is exactly what you need.
The metric side is decimal: 1,000 milligrams make a gram, 1,000 grams make a kilogram, 1,000 kilograms make a metric ton (tonne). The kilogram — the SI base unit of mass — was for over a century defined by a platinum-iridium cylinder kept in Paris; since 2019 it has been defined via the Planck constant, making it reproducible in any well-equipped laboratory on Earth.
The avoirdupois system (the everyday imperial weight system) centers on the pound of 16 ounces. Like the yard, the pound was internationally standardized in 1959: 1 pound is exactly 0.45359237 kilograms, which makes 1 ounce exactly 28.349523125 grams. The stone (14 pounds, about 6.35 kg) survives mainly in the UK and Ireland for body weight — someone who is “11 stone” weighs about 70 kg.
Watch out for two impostors: the troy ounce (31.1 g), used for precious metals and about 10% heavier than the avoirdupois ounce, and the fluid ounce, which measures volume, not mass. This converter uses avoirdupois ounces throughout.
Value in target unit = Value in original unit × (kg per original unit) ÷ (kg per target unit)
Convert to kilograms first using the exact kg factor of the original unit, then divide by the kg factor of the target unit. The 1959 definitions make imperial factors exact to eight decimal places.
Exact kilogram factors in this converter:
Example 1 — Body weight: 150 lb to kilograms. Step 1: 150 × 0.45359237 = 68.0388555 kg. Step 2 is trivial (target is kg): 68.04 kg. The commonly quoted “2.2 lb per kg” shortcut gives 68.18 kg — close, but the exact factor matters for medical dosing.
Example 2 — Baking: 2.5 kg flour to pounds and ounces. Step 1: 2.5 kg stays 2.5 kg. Step 2: 2.5 ÷ 0.45359237 = 5.51156 lb. The 0.51156 lb remainder × 16 = 8.18 oz, so 2.5 kg ≈ 5 lb 8.2 oz — a standard large bag of flour.
Example 3 — UK scale: 11 stone 4 lb to kilograms. Combine first: 11 × 14 + 4 = 158 lb. Step 1: 158 × 0.45359237 = 71.6676 kg. Step 2 is trivial (target is kg): 71.67 kg.
Your airline allows 23 kg checked bags; the home scale reads 52 lb. Convert: 52 × 0.45359237 = 23.5868 kg — over the limit by more than half a kilo, which at many airports triggers a hefty excess fee. Remove a pair of shoes (roughly 1 kg) and reweigh before leaving.
A pediatric dose is 15 mg per kg of body mass, and the child weighs 44 lb. Convert: 44 × 0.45359237 = 19.958 kg ≈ 20 kg. Dose: 20 × 15 = 300 mg. Using the rough 2.2 shortcut (44 ÷ 2.2 = 20 kg) happens to agree here, but for a 33 lb child the shortcut gives 15.0 kg versus 14.97 kg exact — small differences that compound in narrow-therapeutic-index drugs, which is why clinicians use the exact factor.
The oldest known weights — polished stone artifacts from around 3000 BCE — come from the Indus Valley and Egypt, where merchants needed trusted standards for grain and gold. The Romans weighed with the libra (pound), divided into 12 unciae (ounces) — the ancestor of both words “pound” (via libra pondo) and “ounce.” For two millennia, every town had its own pound, and merchants carried conversion tables the way travelers today carry currency apps.
The metric revolution of the 1790s defined the gram as the mass of one cubic centimeter of water at its densest — elegantly linking mass, length, and volume. The kilogram artifact, a platinum-iridium cylinder cast in 1889, served as the world’s mass standard for 130 years despite slowly (and mysteriously) losing about 50 micrograms relative to its copies. In 2019, metrologists finally retired it: the kilogram is now defined by fixing the Planck constant, so any laboratory with a Kibble balance can realize the unit from first principles.
The 1959 agreement that fixed the pound at exactly 0.45359237 kg ended centuries of transatlantic drift between the US and British pounds — a quiet treaty that underpins every international shipment weighed today. The stone, meanwhile, survives as a cultural fossil: Britons still state body weight in stone partly because “11 stone” sounds less clinical than “70 kilograms.”
Example 4 — Produce: 500 g of tomatoes to ounces. Step 1: 500 × 0.001 = 0.5 kg. Step 2: 0.5 ÷ 0.028349523125 = 17.64 oz — just over a pound (16 oz), the standard large tomato pack.
Example 5 — Freight: 2.5 metric tons to pounds. Step 1: 2.5 × 1,000 = 2,500 kg. Step 2: 2.5 ÷ 0.45359237 = 5,511.56 lb. A “2.5-ton” truck rating in metric countries hauls about 5,512 lb — noticeably more than a US 2.5 short-ton rating (5,000 lb).
Example 6 — Jewelry: 1 troy ounce of gold to grams. Careful — this converter uses avoirdupois ounces. A troy ounce is defined separately as exactly 31.1034768 g, about 10% heavier than the 28.35 g kitchen ounce. Gold quoted at $2,000 per troy ounce costs about $70.55 per avoirdupois ounce-equivalent — mixing them misprices bullion.
Useful landmarks when converting body weight between systems:
A conversion is only as good as the measurement feeding it. Kitchen scales should be zeroed (tared) with the empty bowl on them before adding ingredients; weighing flour directly in the mixing bowl eliminates the compaction error of scooping with cups, which can vary by 20% between a light spoon-and-level and a packed scoop. For body weight, weigh at the same time of day — morning after using the bathroom is the standard — because hydration and meals swing readings by 1–2 kg through the day.
Luggage scales deserve skepticism: handheld spring scales are typically accurate to about ±0.2 kg when new but drift with age, so leave a 0.5 kg buffer under the airline limit. Postal scales are the strictest context most people meet — a parcel quoted at 2.0 kg that actually weighs 2.04 kg can jump a price band, so round up when converting for postage. And when a recipe from another country lists “1 stick of butter,” know it means 113 g (4 oz) in the US but 125 g in Australia — convert the sticks, not just the ounces.
Example 7 — Baby weight: 7 lb 6 oz to kilograms. Combine: 7 × 16 + 6 = 118 oz. Step 1: 118 × 0.028349523125 = 3.345 kg. Pediatric growth charts use kilograms, so 3.35 kg is the number the chart wants — and newborn weight is tracked to the gram, making the exact factor essential.
The Weight Converter converts among milligrams, grams, kilograms, metric tons, ounces (avoirdupois), pounds, and stone using exact kilogram factors (1 lb = 0.45359237 kg by the 1959 agreement). Formula: target = value × (kg per from-unit) ÷ (kg per to-unit). Examples: 150 lb = 68.04 kg; 2.5 kg = 5 lb 8.2 oz; 11 st 4 lb = 71.67 kg. Distinguishes mass from weight and avoirdupois from troy ounces.
Exactly 453.59237 grams. The pound was fixed at 0.45359237 kilograms by the 1959 International Yard and Pound Agreement, so multiply pounds by 453.59237 to get grams.
About 35.274 ounces. Compute 1 ÷ 0.028349523125 = 35.27396 oz per kg.
One stone is exactly 6.35029318 kg (14 pounds × 0.45359237). It is still commonly used for body weight in the UK and Ireland.
No. A metric ton (tonne) is 1,000 kg (2,204.6 lb). A US short ton is 2,000 lb (907.2 kg), and a UK long ton is 2,240 lb (1,016 kg). Always check which ton a specification means.
Mass is the amount of matter (kilograms) and never changes with location. Weight is the gravitational force on that mass (newtons) and changes with gravity — you weigh less on the Moon but your mass is identical.
Multiply ounces by 28.3495. For example, 8 oz of flour = 226.8 g. Note that US cups measure volume, so “8 oz” on a measuring cup is fluid ounces — use a scale for accuracy.
Precious metals use the troy ounce (31.1035 g), a survivor of the medieval troy weight system used at the Champagne fairs. It is about 10% heavier than the avoirdupois ounce used for everyday goods.
It is within 0.1%: the true figure is 2.20462 lb/kg. Fine for luggage and gym weights, but use 0.45359237 for medicine, postage thresholds, and engineering.
Cite this page as: Weight Converter. Sigma Calculator. Retrieved October 12, 2026, from https://sigmacalculator.net/math-calculators/weight-converter/
Last updated: October 12, 2026