Weight Converter (kg, g, t, lb, oz, stone, mg)
Type a mass, select the source unit, and see the conversion to every other supported unit at once. Uses internationally agreed conversion factors with full precision.
How it works
How weight conversion works
Every unit pivots through kilograms internally. Since 1959 the international avoirdupois pound is defined as exactly 0.45359237 kg, which fixes ounces (1/16 lb) and stones (14 lb) at exact rationals of the kilogram. The conversion factors are not approximations.
This calculator stores the kilogram-equivalent for each unit and applies value × factor[from] / factor[to]. The only error you'll see is from how many decimal digits you enter and the eight-significant-digit display rounding.
Quick reference
1 kg = 2.2046 lb. 1 lb = 453.59 g. 1 oz = 28.3495 g. 1 stone = 14 lb = 6.35 kg. 1 metric tonne = 1000 kg = 2204.62 lb. UK body weight is often given in stone-and-pounds (e.g., '11 stone 4' = 158 lb = 71.7 kg).
Watch out for two different 'tons' — the metric tonne (1000 kg, used here) versus the US short ton (907.18 kg) and UK long ton (1016.05 kg). They differ by ~10%, which is enough to make shipping invoices wrong.
Common pitfalls
Cooking measurements: an ounce of flour is by weight, not by volume. The 'fluid ounce' (fl oz) is a volume unit and isn't on this calculator — use a volume converter instead.
'Pound force' vs 'pound mass': in physics contexts these are different. The pound here is mass (lb_m). Pound force (lb_f) is mass × gravity and isn't a length unit any more than newtons are kilograms.
Troy ounces (used for precious metals) differ from avoirdupois ounces by about 10%: 1 troy oz = 31.1035 g vs 1 avoirdupois oz = 28.3495 g. This calculator uses the everyday avoirdupois system.
Frequently asked questions
›Are these conversions exact?
Yes. Since 1959 the international pound is defined as exactly 0.45359237 kg, making all imperial-to-metric conversions exact rationals.
›What's the difference between US and UK tons?
US short ton = 907.185 kg. UK long ton = 1016.05 kg. Metric tonne (used here) = 1000 kg. Always check which is meant in shipping documents.
›Are troy ounces supported?
Not yet — this tool uses everyday (avoirdupois) ounces. For precious metals, multiply the troy ounces by 31.1035 to get grams.
›Can I weigh fluids?
Mass and volume are different. For fluids, use a volume converter, then multiply by the liquid's density to get mass.
›Why doesn't kg = pound × 2.2 give the same answer as your tool?
1 kg = 2.20462262... lb. The shortcut 'kg × 2.2' is fast but loses about 0.2% accuracy; use the calculator for anything that matters.
›Is this accurate for shipping or freight?
Eight significant digits is more than enough for shipping. For very high precision (e.g., precious metals trading), refer to NIST official factors.
›What's the smallest unit?
Milligrams. For micrograms or below, multiply the milligram result by 1000.
›Does the calculator work offline?
Yes — once the page is loaded, all conversions run in your browser.
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