How it works
Every unit is defined as a ratio to a base unit for its category — metres for length, kilograms for weight, litres for volume, and so on. The calculator converts your value into the base unit, then from the base unit into the unit you want. Temperature uses formulas rather than simple ratios because its scales have different zero points.
°F = °C × 9/5 + 32 · K = °C + 273.15
Worked example
To convert 5 miles to kilometres: 5 × 1609.344 m = 8046.72 m, divided by 1000 m per km gives 8.047 km.