Weight Converter (kg, g, t, lb, oz, stone, mg)

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.