A conversion is a mapping, not a single number.
Most converters give you one figure and hide the relationship. These show both scales laid alongside each other, so you can see how the units line up — and read off the neighbouring values while you're there.
1 in = 2.54 cm
Every converter here reports like this. Type in either field and both scales move together.
Popular conversions
The questions people ask most, each with a full chart: Celsius to Fahrenheit chart, mpg to L/100km chart, L/100km to mpg, mph to knots, knots to mph and km/h, oven temperatures and gas marks, 180 cm in feet and inches and the kitchen conversion chart.
Sixteen converters, calculators and charts
Each runs entirely in your browser. Nothing you type is sent anywhere.
How these are built
Exact factors where exact factors exist, and a note where they don't.
Most imperial units are defined in terms of metric ones, and have been since the international yard and pound agreement of 1959. An inch is exactly 25.4 mm. A pound is exactly 0.45359237 kg. These are definitions rather than measurements, so the conversions carry no rounding error at all, and the reference tables on this site are exact.
Where a unit genuinely is ambiguous — the three tons, the two gallons, the four different cups — the page says so plainly instead of silently picking one. That ambiguity is the actual cause of most conversion mistakes, and it is worth more than another decimal place.
Nothing you enter leaves your device. There are no accounts and no saved history; the arithmetic happens in JavaScript on the page in front of you.