How to use this calculator

1. Pick a category — length, mass, temperature, and so on.
2. Enter the value you want to convert and choose its unit.
3. Choose the unit to convert to.
4. The result updates instantly; use the swap button to reverse the direction.

How it works

Most unit conversions work by passing through a common base unit. Every length, for example, can be expressed in meters: to convert 5 miles to kilometers, the converter first turns miles into meters (1 mile = 1609.344 m), then meters into kilometers. This "convert to the base unit, then to the target" approach keeps every conversion in a category consistent and perfectly reversible.

Temperature is the exception. Because Celsius, Fahrenheit, and Kelvin don't share a zero point, they convert with formulas rather than a single multiplier — for instance $F = C \times 9/5 + 32$. The converter applies the right formula automatically, so you never have to remember which one to use.

Worked example

To convert 100 kilometres per hour to miles per hour, the tool goes through the base unit (metres per second) and back: $100 \text{ km/h} \approx 62.14 \text{ mph}$. Hit the swap button and 60 mph comes back as about 96.56 km/h.