Everyday weights sit on a single exact definition: since 1959 the avoirdupois pound has been 0.45359237 kilograms, and every ounce, stone and short ton follows from it. The trap in this category is that more than one system shares the same words — a troy ounce of gold is not the ounce on a kitchen scale, and a fluid ounce is not a mass at all.
Tools in this category
Ounces to Grams
Convert ounces to grams in your browser, with a warning about fluid ounces, which measure something else entirely.
Pounds to Kilograms
Convert pounds to kilograms in your browser. A pound is exactly 0.45359237 kilograms, fixed by agreement in 1959.
Kilograms to Pounds
Convert kilograms to pounds in your browser. One pound is exactly 0.45359237 kilograms, the value fixed by the international yard and pound agreement.
Grams to Ounces
Convert grams to ounces for recipes and postage. One avoirdupois ounce is a sixteenth of a pound, which works out at 28.349523125 grams exactly.
Milligrams to Grams
Convert milligrams to grams in your browser. The SI prefix milli means one thousandth, so 1 mg is exactly 0.001 g.
Tonnes to Kilograms
Convert metric tonnes to kilograms. A tonne is exactly 1000 kg, which is neither the 2000 lb short ton nor the 2240 lb long ton.
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What should it convert, calculate or generate, and where would the authoritative numbers come from? A link to the standard or publication that defines them is the most useful thing you can send.
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How these tools are built
Every tool in this category runs entirely in your browser: there is no upload, no account and no request to a server once the page has loaded. The numbers behind them are transcribed from the organisation that defines them — NIST for units, the W3C for web formats, the WHO for health measures — and each page names its source next to the formula. A tool whose reference values stop reproducing fails the build and does not ship, which is the whole reason the catalogue grows slowly.