Weight Converter

How It Works

This weight converter uses grams (g) as its internal base unit. Every unit has a stored factor equal to the number of grams it contains: a kilogram = 1,000 g, a milligram = 0.001 g, a metric ton = 1,000,000 g. To convert from unit A to unit B, the tool multiplies the input by A's gram-factor, then divides by B's gram-factor.

The metric system defines mass through the kilogram (kg), which has been the SI base unit since 1889 when the International Prototype of the Kilogram — a platinum-iridium cylinder — was created. In 2019, the kilogram was redefined in terms of the Planck constant, making it more stable and reproducible. The gram (g) is simply one thousandth of a kilogram.

Imperial and US customary weight units trace back centuries. The pound (lb) derives from the Roman libra pondo ("pound weight"). The avoirdupois pound — the one used in everyday trade in the US and UK — equals exactly 453.59237 grams by international agreement since 1959. The ounce (oz) is one-sixteenth of a pound = 28.3495 g.

The stone is a unit still used in the United Kingdom and Ireland for body weight. One stone = 14 pounds = 6.35029 kg. To convert "11 stone 5 pounds" to kilograms: (11 × 14 + 5) = 159 lb × 0.453592 = 72.12 kg.

Worked example — Convert 70 kg (body weight) to pounds:
70 × 1000 g/kg ÷ 453.592 g/lb = 154.324 lb

Worked example — Convert 500 g to ounces:
500 ÷ 28.3495 = 17.637 oz

Worked example — Convert 2.5 metric tons to pounds:
2.5 × 1,000,000 g ÷ 453.592 g/lb = 5,511.56 lb

Note on terminology: "weight" and "mass" are often used interchangeably in everyday language, but scientifically, mass is the amount of matter (measured in kg) and weight is the gravitational force on that mass (measured in Newtons). Scales on Earth measure force and display mass; this tool works in mass units as used in daily life, cooking, commerce, and fitness.

Precision: results are computed to 10 significant figures and trailing zeros are removed. For very large or small values the result uses scientific notation.