Weight and Mass Converter

Mass vs weight

In everyday use "weight" means mass, measured in kilograms or pounds. In physics, weight is a force (newtons or pound-force) equal to mass × gravity. A 1 kg mass weighs 9.80665 N under standard gravity.

Three different ounces

The avoirdupois ounce (28.349523125 g) is used for food and parcels, the troy ounce (31.1034768 g) for precious metals, and the US fluid ounce (29.5735 mL) measures volume, not mass.

Weight and Mass unit definitions

kilogram (kg)

The kilogram (kg) is the SI base unit of mass. Since 2019 it is defined by fixing the Planck constant, replacing the platinum-iridium prototype kept near Paris.

gram (g)

The gram (g) is one thousandth of a kilogram. It is the everyday unit for food portions, recipes and small items.

milligram (mg)

The milligram (mg) is one thousandth of a gram. It is the standard unit for medicine doses and supplement labels.

microgram (µg)

The microgram (µg, often written mcg on labels) is one millionth of a gram.

metric ton (t)

The metric ton or tonne (t) is 1000 kilograms. It is accepted for use with the SI.

pound (lb)

The avoirdupois pound (lb) is exactly 0.45359237 kg. It is the everyday unit of weight in the United States. Reference: Avoirdupois system: 1 lb = 16 oz = 7000 grains = 0.45359237 kg exactly (1959 agreement).

ounce (oz)

The avoirdupois ounce (oz) is 1/16 of a pound, exactly 28.349523125 g. It is not the same as the troy ounce used for gold or the fluid ounce used for volume. Reference: Avoirdupois system: 1 lb = 16 oz = 7000 grains = 0.45359237 kg exactly (1959 agreement).

stone (st)

The stone (st) is 14 pounds, exactly 6.35029318 kg. It is still used for body weight in the UK and Ireland, often as stones and pounds. Reference: Avoirdupois system: 1 lb = 16 oz = 7000 grains = 0.45359237 kg exactly (1959 agreement).

short ton (ton (US))

The short ton is 2000 pounds, exactly 907.18474 kg. In the United States it is simply called the ton. Reference: Avoirdupois system: 1 lb = 16 oz = 7000 grains = 0.45359237 kg exactly (1959 agreement).

long ton (ton (UK))

The long ton (imperial ton) is 2240 pounds, exactly 1016.0469088 kg. Reference: Avoirdupois system: 1 lb = 16 oz = 7000 grains = 0.45359237 kg exactly (1959 agreement).

grain (gr)

The grain (gr) is exactly 64.79891 mg. It is identical in the avoirdupois, troy and apothecaries systems. Reference: Avoirdupois system: 1 lb = 16 oz = 7000 grains = 0.45359237 kg exactly (1959 agreement).

troy ounce (oz t)

The troy ounce (oz t) is 480 grains, exactly 31.1034768 g, about 10 % heavier than the ordinary ounce.

carat (ct)

The metric carat (ct) is exactly 200 mg. It measures gemstone mass; the karat (K) for gold purity is a different thing.

All weight and mass conversions

Related converters

• Volume Converter – L, mL, m³, ft³, in³, US gal, imp gal
• Length Converter – m, km, cm, mm, µm, ft, in, mi, yd, nmi
• Pressure Converter – Pa, kPa, psi, bar, inH₂O, mmHg, torr, atm
• Printable weight and mass conversion chart – print, PDF or PNG
• liters to gallons (volume, not weight)
• psi (pound-force per square inch) to kPa

Sources

• The International System of Units (SI), 9th edition (SI Brochure), Bureau International des Poids et Mesures.
• Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 2008 Edition, National Institute of Standards and Technology.

Last reviewed: 2026-10-15.