📏 Length Unit Converter
Convert between mm, cm, m, km and more.
How Length Conversion Works
Metric units step by powers of ten: 10 mm make a centimetre, 100 cm a metre and 1,000 m a kilometre. Imperial units are not decimal — 12 inches make a foot, 3 feet a yard and 1,760 yards a mile — so conversions need a fixed multiplier instead of a decimal shift. The international definitions are exact: since 1959 the inch has been 25.4 mm, which fixes the foot at 30.48 cm and the mile at 1.609344 km.
Basic Conversions
To convert in either direction, multiply or divide by the factor: 1 inch = 2.54 cm means inches × 2.54 = centimetres, and centimetres ÷ 2.54 = inches.
Worked Examples
1.75 m = 175 cm = 5 ft 8.9 in (175 ÷ 30.48 = 5.74 ft).
A 26.2-mile marathon = 26.2 × 1.609344 = 42.195 km.
Precision and Rounding
Metric prefixes are exact powers of ten, but imperial conversions are rounded when displayed. Rounding in the middle of a calculation compounds the error, so convert once from the original unit. Note that the US survey foot and the nautical mile differ slightly from the international units used here.
Frequently Asked Questions
- How many centimetres are in an inch?
- Exactly 2.54 cm, by international agreement since 1959.
- How do I convert metres to feet and inches?
- Divide by 0.3048 to get feet, then multiply the fractional part by 12: 1.75 m ÷ 0.3048 = 5.74 ft = 5 ft 8.9 in.
- Is a mile the same in the US and the UK?
- Yes for the international mile (1,609.344 m). The US survey mile, kept only for legacy land records, is 1,609.347 m — about 3 mm longer.