Weight Converter

Weight and mass are technically different: mass measures the amount of matter in an object, while weight measures the gravitational force acting on that mass. On Earth's surface they are functionally equivalent, but an astronaut who weighs 80 kg on Earth would weigh about 13 kg on the Moon — while their mass stays the same. In everyday language, we use "weight" to mean both.

The metric system uses grams and kilograms. One kilogram was originally defined as the mass of one liter of water at 4°C. Since 2019 it has been redefined in terms of Planck's constant, a fundamental physical quantity, making it independent of any physical artifact. Most of the world uses kilograms for body weight, grocery shopping, and commercial goods.

The United States uses pounds and ounces, inherited from the British imperial system. The UK officially uses kilograms in commerce but many British people still think in "stone" for body weight — a unit of 14 pounds used almost nowhere else in the world. For international shipping, aviation cargo, and global trade, kilograms are the universal standard.

Weight conversions are essential for international travel (airline baggage limits are often in both kg and lbs), cooking foreign recipes (European recipes use grams, American recipes use cups and ounces), medication dosing which is always in milligrams and grams regardless of country, and online shopping from international retailers whose sizing charts may reference weight in unfamiliar units.