Weight Converter

What mass and weight measure

In everyday speech weight usually means mass, that is how much matter a body contains. The SI base unit is the kilogram (kg). Since 2019 it has been defined through the Planck constant rather than a physical artefact.

Main units and where they are used

• Gram (g) – food, medicine and postal items; kilogram (kg) – body weight and shopping.
• Tonne (t, 1000 kg) – freight and industry.
• Pound (lb, 0.45359237 kg) and ounce (oz, 28.3495 g) – the USA and United Kingdom.
• Stone (6.35 kg) – body weight in the UK.

Common pitfalls

Different tons: the metric tonne is 1000 kg, the US short ton about 907 kg and the British long ton about 1016 kg. Precious metals use the troy ounce (31.1035 g), which differs from the ordinary ounce. In physics weight is actually a force, measured in newtons, not kilograms. For everyday conversions this does not matter, but it is worth keeping apart when solving problems.