Weight & Mass Converter

Mass versus weight, and what the tool really converts

Strictly, kilograms, grams and pounds are units of mass, while weight is the force gravity puts on that mass. On Earth the two are used interchangeably, and so does this page: it converts mass between ten units (mg, g, kg, tonne, oz, troy oz, lb, st, US short ton and long ton) through the gram. The pound is defined from the kilogram, not the other way round: 1 lb = 0.45359237 kg exactly, from the same 1959 agreement that defined the yard. An ounce is one sixteenth of that, 28.349523125 g, and a stone is 14 lb, 6.35029318 kg.

Worked examples

• 70 kg to pounds: 70 / 0.45359237 = 154.32 lb.
• 11 st 4 lb is (11 × 14 + 4) = 158 lb, which is 71.668 kg. Convert the stone and pound parts to one unit first, because the tool takes a single value.
• A recipe asking for 8 oz is 8 × 28.349523125 = 226.8 g.
• One US short ton is 2,000 lb, or 907.18 kg. A metric tonne is 1,000 kg, which is 2,204.62 lb.

Pitfalls specific to weight

• Avoirdupois versus troy. The ounce here is the ordinary avoirdupois ounce used for food and body weight. Gold, silver and other precious metals trade in troy ounces of 31.1034768 g, about 9.7% heavier, and it is a separate unit here (Troy ounce, oz t). Using the wrong ounce on a bullion price is a classic error.
• Three different tons. The tool offers the metric tonne (1,000 kg), the US short ton (2,000 lb) and the British long ton of 2,240 lb (1,016.05 kg), which suits ships' displacement and older UK documents.
• Stone is regional. It is mainly a UK and Ireland body-weight unit, and this page uses 14 lb for one stone.
• Pound-force. Engineering specs sometimes use lbf, a force. It is not interchangeable with lb of mass outside Earth's surface gravity.

Handy equivalents

If you are converting a body weight for a health formula, the BMI calculator accepts the units directly, and the unit converter has the same weight list alongside the other categories.