Seven categories — length, weight, temperature, area, volume, speed and time — with the units people reach for rather than every unit that exists.
Each conversion goes through one base unit: your figure is converted into metres, kilograms or kelvin, then out again into whatever you asked for. That means adding a unit can never break an existing pair, and the two directions always agree with each other.
Because temperature scales have an offset, not just a different step size. Fahrenheit starts 32 degrees below Celsius, so you multiply by 9/5 and then add 32 — 20 °C is 68 °F. Multiplying alone is the single most common conversion mistake, which is why this tool does not quote a rate for temperature.
US. A US gallon is 3.785 litres; an imperial gallon is 4.546 litres, about 20% larger. Recipes and fuel figures from the UK use the imperial one, so a number that looks a fifth out is usually this.
They are not fixed durations. A month is 28 to 31 days and a year is 365 or 366, so any single factor would be wrong most of the time. Use the Date Calculator, which counts the actual calendar.
The definitions are. An inch is exactly 0.0254 metres and a pound is exactly 0.45359237 kilograms by international agreement, so nothing is approximated on the way in. Only the displayed result is rounded, to about eight significant figures.
Every other category is a plain multiplication. Temperature has an offset, so stopping at 36 would be wrong by 32 degrees.
Conversions use the international definitions. Volume measures are US, not imperial. Nothing you type here is sent to our servers — the calculation runs entirely in your browser.
