Conversion Calculator

Weight conversion, like length, hangs on one exact definition: the international avoirdupois pound is exactly 453.59237 grams. Every imperial weight unit derives from it. An ounce is one-sixteenth of a pound, so 28.349523125 g exactly. A stone — still used in the UK and Ireland for body weight — is 14 pounds, or 6,350.29318 g. The converter normalizes through grams, so these exact factors mean a value can round-trip through any unit without accumulating error.

The metric side is decimal again: a milligram is a thousandth of a gram, a kilogram a thousand grams, and a metric tonne a million grams (1,000 kg). Most everyday weight lives in the gram-to-kilogram range, and the only thing to watch is keeping the decimal place straight — 2.5 kg is 2,500 g, not 250 g.

For quick mental math, one kilogram is about 2.205 pounds, and one pound is about 454 grams — close enough to "half a kilo" that recipes often treat 500 g and 1 lb as interchangeable, though they differ by about 10%. One ounce is roughly 28 grams. These approximations are fine for cooking; for anything that has to be exact — shipping weights, dosages, scientific work — use the full factors the converter carries.

The pitfall here is the word "ounce." The ounce on this converter is the avoirdupois ounce, the one used for weight. It is not the fluid ounce, which measures volume, and it is not the troy ounce used for precious metals (a troy ounce is about 31.1 g, heavier than the everyday ounce). If you're weighing gold or measuring a liquid, you want a different unit — the volume converter handles fluid ounces, and troy weights aren't included here precisely because mixing them up is how mistakes happen.