Unit converter

13 categories, 134 units. Every number on this site comes out of one table, so no two pages can disagree.

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LengthDistance, from nanometres to light years. Weight and MassMass, from micrograms to tons. VolumeCapacity, including the kitchen measures that differ between countries. AreaSurface area, from square millimetres to square miles. SpeedHow fast, in every unit people actually use. TimeFrom nanoseconds to centuries. PressureForce per unit area, for tyres, weather and engineering. EnergyEnergy and work, including the two different calories. PowerRate of energy, including the three different horsepowers. Data StorageBytes, and the decimal-versus-binary difference that makes your drive look smaller. AngleDegrees, radians and the ones surveyors use. TemperatureCelsius, Fahrenheit and Kelvin. The only common category where you cannot just multiply. Fuel economyMiles per gallon, kilometres per litre and litres per 100 km — two of which run backwards from the third.

Why another one of these

Most converters hand you a number with no idea how much to trust it. A US cup and an imperial cup are different sizes. A food calorie is a thousand physics calories. A "1 TB" drive reports 931 GB. Mach 1 is slower when it is cold. Three different horsepowers are in daily use and they disagree.

Every unit here carries a line saying what it actually is — exact by definition, an average, or something that shifts with conditions. That line is usually the answer you came for.