Length converter
Convert between metric and imperial length units.
Fill in the fields and the result will appear here automatically.
Converts length between metric and imperial units: millimetres, centimetres, metres, kilometres, inches, feet, yards, miles and nautical miles. Unit factors are exactly defined; calculation and result display have finite precision.
How it works
Formula and logic
Every unit has an exact factor to the metre, and conversion goes through that base.
Example
1 inch is exactly 2.54 cm, and 1 mile is exactly 1609.344 m.
Fields and units
- Value — in the selected source unit
- From unit — list option
- To unit — list option
How to use
- — Enter the value.
- — Pick the source unit.
- — Pick the target unit.
Method and limitations
- Calculation method
- Formula and logic
- Data or methodology source
- NIST: international and historical US survey foot NIST: conversion-factor tables, Appendix B.9 BIPM: SI Brochure, version 4.01 (2026)
- Limitation
- The result is a rounded unit conversion. Check the entered value and selected units.
FAQ
Are imperial conversions exact?
This uses international definitions: 1 inch = 0.0254 m and 1 foot = 0.3048 m. The defining factors are exact, but the numerical display is rounded. The historical US survey foot is not included.
What is a nautical mile?
Exactly 1852 metres, used in sea and air navigation. It is longer than the statute mile of 1609.344 m.
Does the converter work both ways?
Yes. Swap the source and target unit and the conversion runs in the opposite direction.
Why does the same unit return the value unchanged?
Converting a unit to itself skips the base entirely, so no floating-point drift is introduced.