Unit Converter

Features

• Eight measurement families covering 60+ units
• Bidirectional, type into either box
• A full conversion table showing every unit at once
• Swap the two units with one click
• Precision preserved to 12 significant figures

How to use it

1. Choose what you are converting.
2. Pick the source and target units.
3. Type into either box, the other updates.
4. Scroll down for the same value in every unit.

How the conversions are calculated

Every unit in a family is defined by its ratio to one base unit, metres for length, kilograms for mass, litres for volume. Converting from A to B means multiplying by A's ratio and dividing by B's. Chaining through a single base rather than storing every possible pair keeps the table small and, more importantly, keeps it consistent: there is no way for the metre-to-foot factor to disagree with the foot-to-metre one.

The factors are exact where exact values exist. Since 1959 the international yard has been defined as precisely 0.9144 metres, which makes the inch exactly 25.4 millimetres and the mile exactly 1,609.344 metres. The pound is exactly 0.45359237 kilograms. These are definitional, not measured, so the only error is floating-point rounding.

A few unit names are genuinely ambiguous and worth checking before you rely on a result. The US gallon (3.785 L) and imperial gallon (4.546 L) differ by 20%, and the same applies to pints and fluid ounces, this tool labels both explicitly. The ton is worse: a US short ton is 907 kg, a UK long ton is 1,016 kg, and a metric tonne is 1,000 kg. Digital storage carries its own ambiguity, covered in the file size converter.