Length Converter

Reviewed by the CalculatorHub team, edited by James Graham. NIST-defined conversion factors. Last verified 13 June 2026.

Length and distance measurements span a vast range of scales and a wide variety of units across different countries and disciplines. The metric system, defined by the International System of Units (SI) and anchored by the metre as the base unit, is the standard in science and in most of the world, while the United States and a handful of other countries continue to use the imperial system of inches, feet, yards, and miles for everyday purposes. The definitions are exact under modern standards: one inch equals exactly 0.0254 metres, one foot equals exactly 0.3048 metres, one yard equals exactly 0.9144 metres, and one international mile equals exactly 1,609.344 metres. The nautical mile, used in maritime and aviation contexts, equals exactly 1,852 metres by international convention. Converting between units is a matter of multiplying by the appropriate conversion factor, but keeping track of those factors for every combination is tedious. This calculator displays nine common length units simultaneously: millimetres, centimetres, metres, kilometres, inches, feet, yards, miles, and nautical miles. Type a value into any field and all the others update instantly. Conversion factors are sourced from NIST Handbook 44 and NIST Special Publication 330, the authoritative US references for weights and measures definitions. Use the calculator for any length or distance conversion, from converting a recipe's metric measurements to adjusting architectural dimensions.