Weight / Mass Converter

How it works

Weight (technically mass) conversions translate between metric (milligrams, grams, kilograms, metric tons) and imperial/US customary (ounces, pounds, stones). The pound is defined as exactly 0.45359237 kilograms — a definition agreed internationally in 1959. From that, 1 kg ≈ 2.205 lb, and 1 oz = 28.3495 g.

Some conversions you'll use a lot: 1 kg = 2.205 lb; 1 lb = 16 oz = 453.6 g; 1 stone = 14 lb = 6.35 kg (used for body weight in the UK and Ireland but rarely elsewhere); 1 metric ton = 1000 kg ≈ 2,205 lb; 1 short ton (US) = 2,000 lb = 907 kg; 1 long ton (UK) = 2,240 lb = 1,016 kg.

Notice the three different "tons": metric (1000 kg), short (US, 907 kg), and long (UK, 1016 kg). They differ by ~10% so always specify which one. Most modern usage is metric or short ton; the long ton is mostly historical.

Pharmacology uses milligrams (mg) and micrograms (μg) for drug doses. Cooking weights in the US use ounces and pounds; in the UK and most of the world, grams and kilograms. Recipe conversions: a "stick" of butter in the US is 4 oz = 113 g, a US cup of flour is roughly 120–130 g.

In casual usage, "weight" and "mass" are used interchangeably, but they're different concepts. Mass is the amount of matter (kg, lb-mass); weight is the force gravity exerts on that mass (newtons, pound-force). On Earth's surface they convert with a factor of 9.81 m/s². On the Moon you'd weigh ~1/6 of your Earth weight but your mass would be unchanged. For everyday use this distinction rarely matters.