Length Converter
Convert distance between nine units. Every unit is defined from the international metre, so the factors are exact rather than approximated.
All units
How to use the Length Converter
- Type the value you want to convert.
- Pick the unit you are converting from and the unit you want.
- The result updates as you type, and the table below shows every other unit at once.
Exact conversion factors
Since 1959 the inch has been defined as exactly 0.0254 metres by international agreement. Every other imperial length follows from it, which makes these conversions exact rather than approximate:
| Unit | Exactly |
|---|---|
| 1 inch | 25.4 mm |
| 1 foot | 0.3048 m (12 inches) |
| 1 yard | 0.9144 m (3 feet) |
| 1 mile | 1,609.344 m (1,760 yards) |
| 1 nautical mile | 1,852 m |
The nautical mile is the odd one out: it is defined from the Earth rather than from the metre, as one minute of latitude. That is why it is a round number of metres and an awkward number of feet, and why it remains standard in aviation and shipping.
Quick mental conversions
- cm to inches — divide by 2.5 and add a little. 10 cm ≈ 4 inches.
- metres to feet — multiply by 3 and add 10%. 10 m ≈ 33 ft.
- km to miles — multiply by 0.6, or use consecutive Fibonacci numbers: 5 km ≈ 3 miles, 8 km ≈ 5 miles, 13 km ≈ 8 miles.
- miles to km — multiply by 1.6.
The Fibonacci trick works because the ratio between consecutive terms approaches 1.618, and a mile is 1.609 km. It is accurate to within about half a percent.
Frequently asked questions
Why is a nautical mile different from a mile?
It is defined as one minute of latitude — 1,852 metres — so it maps directly onto navigational charts. A statute mile is a land measure with no relationship to the Earth's geometry.
Are US and UK measurements the same?
For length, yes since 1959. Both use the international inch of exactly 25.4 mm. Volume is where they diverge: a US gallon and an imperial gallon are quite different.
Why does my result show many decimal places?
Most conversions between metric and imperial produce non-terminating decimals. Results are rounded for readability and the exact working is shown underneath.
What is a survey foot?
A slightly different US definition used in land surveying, longer than the international foot by about two parts per million. It was officially retired at the end of 2022 but appears in older land records.
Related tools
Convert between kilograms, pounds, ounces, stone and tonnes.
Convert Celsius, Fahrenheit, Kelvin and Rankine.
Convert km/h, mph, m/s, knots and Mach.
Convert bytes, kilobytes, megabytes and their binary equivalents.
Body mass index in metric or imperial, with category ranges.