Length converter
Convert between millimetres, centimetres, metres, kilometres, inches, feet, yards, miles and nautical miles. Exact factors, in your browser.
Runs in your browser
Every length unit, one page
Pick any two units above. For the conversions people look up most often there are dedicated pages with reference tables, linked below.
The factors are exact
Since the international yard and pound agreement of 1959, the imperial units have been defined in terms of the metre rather than measured against it. Every factor here follows from that definition, so nothing is rounded:
| Unit | Metres | Note |
|---|---|---|
| Millimetre | 0.001 | |
| Centimetre | 0.01 | |
| Metre | 1 | SI base unit |
| Kilometre | 1000 | |
| Inch | 0.0254 | exact by definition |
| Foot | 0.3048 | 12 inches |
| Yard | 0.9144 | 3 feet |
| Mile | 1609.344 | 1760 yards |
| Nautical mile | 1852 | exact, but not derived from the yard |
The nautical mile is the odd one out
Every imperial unit above descends from the inch. The nautical mile does not. It was defined as one minute of latitude along a meridian, and is now fixed at exactly 1852 metres by international agreement. That is why it does not divide neatly into miles or feet, and why speed at sea is measured in knots, one nautical mile per hour, rather than in miles per hour.
Where people go wrong
A US survey foot is not a foot. Until 2022 the United States maintained a separate survey foot, longer than the international foot by two parts per million. It is negligible over a room and significant over a state boundary. This converter uses the international foot.
Squared and cubed units do not share these factors. A square metre is not 3.28 square feet; it is 3.28 squared, which is 10.76. Use the area and volume converters rather than squaring a length conversion by hand.