Weight & Mass Converter
Convert between metric and imperial weight units — milligrams, grams, kilograms, ounces, pounds, stone, metric tons, and short tons.
How to use this converter
Pick the unit you're starting from on the left, the unit you want on the right, and type a value. The converted figure updates as you type. Hit the swap button (⇄) to flip the direction instantly — useful when you've picked the wrong way around.
The eight units covered
Metric: milligram (mg), gram (g), kilogram (kg), metric ton (t = 1000 kg). All powers of ten apart, so scaling between them is just shifting decimal places. Imperial / customary: ounce (oz), pound (lb = 16 oz), stone (st = 14 lb), short ton (ston = 2000 lb). The relationships within imperial are not powers of ten — just memorise them or rely on the calculator.
The keystone conversions
1 lb = 453.59237 g (defined exactly in 1959). 1 oz = 28.35 g (also exact, 1/16 of a pound). 1 kg ≈ 2.205 lb — useful for body weight, food, freight. 1 stone = 14 lb = ~6.35 kg — UK body-weight convention. 1 short ton = 2000 lb ≈ 907 kg — US freight and aggregate measure, ~10% lighter than a metric ton.
Where these conversions matter
Travel: airline baggage allowances quoted in kg or lb (and the difference between an extra-bag fee and a free bag). Shipping: freight quoted by weight class — metric ton vs short ton swings invoices by ~10%. Cooking: ingredient weights in recipes from different regions. Fitness: body weight, plate weights on barbells (kg outside the US, lb inside), supplement doses (mg of caffeine, g of protein).
Why pounds and ounces in the same system
The avoirdupois system divides a pound into 16 ounces, mostly because 16 is divisible by 2 four times — useful for halving and quartering a quantity by hand long before decimal scales existed. The metric system was designed later (1790s, France) specifically to avoid these awkward base numbers, which is why scientific and most international measurements use kg and g exclusively.
Frequently asked questions
What's the difference between metric ton and short ton?▾
A metric ton (or tonne) is exactly 1000 kg, used worldwide and in scientific contexts. A short ton is the customary US ton — 2000 lb, or about 907 kg. The two differ by about 10%. The UK historically used a long ton (2240 lb ≈ 1016 kg) but has mostly switched to metric tons; the calculator only includes the short ton, which is the one still in active commercial use in the US.
Why does the calculator distinguish weight from mass?▾
Strictly, mass (kg, lb-mass) is the amount of matter in an object — constant everywhere. Weight is the force gravity exerts on that mass — an astronaut weighs less on the Moon. Everyday usage conflates the two, and so does this calculator: kg, lb, oz, and stone are all treated as units of mass. The conversions are mathematically identical to weight conversions on Earth, where g is roughly constant.
Why is one stone = 14 pounds?▾
Historical convention. The stone is a UK unit traditionally used for body weight (a person weighing "12 stone 4" weighs 172 lb). It was standardised at 14 lb in the 19th century — before that, regional "stones" varied wildly (different stones for cheese, hay, and lead). Outside the UK and Ireland, body weight is typically given in kg or lb, not stone.
What's the easiest way to estimate kg ↔ lb in my head?▾
Multiply kg by 2.2 (or divide by 0.45). 70 kg ≈ 154 lb. Going the other way, divide lb by 2.2 — 200 lb ≈ 91 kg. For more precision: 1 kg = 2.20462 lb. The difference between 2.2 and 2.20462 is small — about 0.2% — so the rule of thumb is fine for everyday estimates.
Is the avoirdupois ounce the same as a fluid ounce?▾
No — they measure different things. The avoirdupois ounce (used here) is a unit of mass: 28.35 g. The fluid ounce is a unit of volume: roughly 29.6 mL in the US, 28.4 mL in the UK. They're named confusingly because a fluid ounce of water happens to weigh roughly an ounce — but for any other liquid, the relationship breaks. For volume conversions, use the unit converter or a dedicated volume tool.
Are the conversion factors exact?▾
Yes — they all derive from the 1959 international yard and pound agreement. 1 lb = exactly 0.45359237 kg, 1 oz = exactly 28.349523125 g, 1 stone = exactly 14 lb, 1 short ton = exactly 2000 lb. These are agreed-upon definitions, not measurements. Display rounds to 6 significant digits, which is plenty for any practical use.
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