Unit converter

Converting between units

Pick a category, type a value and the conversion appears as you type. Five categories are covered: length, weight, temperature, volume and energy — the ones that actually come up when reading a recipe, a spec sheet or a foreign parcel label.

Everything except temperature converts through a base unit, so the result is exact to the precision of the definition: an inch is exactly 25.4 mm, a pound exactly 0.45359237 kg. Temperature has its own formulas because the scales have different zero points.

The swap button flips the two units, which is the fastest way to check a conversion the other way round. Small results are shown to six decimal places, large ones to two.

Frequently asked questions

Why is temperature handled differently?

Because zero Celsius is not zero Fahrenheit. Multiplying by a factor works for length or weight, but temperature also needs a shift: °F = °C × 9/5 + 32, and kelvin is Celsius plus 273.15.

Are the pints and gallons US or imperial?

US. A US gallon is 3.785 litres, an imperial gallon 4.546 — a difference of a fifth, which matters for fuel figures. The cup is the 240 ml one used in American recipes.

Where would I need kilojoules?

On food labels: the EU prints kJ, most other countries print kcal. One kilocalorie is 4.1868 kJ, so a 2,000 kcal daily intake is about 8,370 kJ.

How exact are the results?

The maths runs at full double precision; only the display is rounded. The copy button gives the value at the shown precision, which is enough for anything short of a laboratory.