Length Converter
Convert between metric and imperial length units — mm, cm, m, km, inches, feet, yards, and miles. Instant results with one click.
How to calculate Length
Length conversion is one of the most common calculations in everyday life — from reading a foreign blueprint to following a recipe that uses different units than you are used to.
The metric system is built on powers of ten: 10 mm = 1 cm, 100 cm = 1 m, 1000 m = 1 km. This makes metric-to-metric conversion trivial — just move the decimal point.
Imperial conversions are less regular: 12 inches = 1 foot, 3 feet = 1 yard, 1760 yards = 1 mile. Converting between metric and imperial requires fixed ratios: 1 inch = 2.54 cm exactly (by international treaty since 1959).
Key conversions to know: 1 m = 3.281 ft, 1 km = 0.621 mi, 1 ft = 30.48 cm, 1 mi = 1.609 km.
Engineering, construction, and navigation all rely on precise length conversion. The Mars Climate Orbiter was lost in 1999 due to a software error mixing metric and imperial units — a $327 million reminder that unit conversion matters. This calculator handles all eight common length units with six decimal places of precision.