Converters
Length Converter
Convert between metric and imperial length units: millimetres, centimetres, metres, kilometres, inches, feet, yards, miles and nautical miles. The result appears in every unit at once.
How to use this converter
- Enter the value you want to convert.
- Choose the unit you are converting from and the unit you want.
- Use Swap to reverse the direction. The table below shows the same value in every unit.
Formula
Result = Value × (factor of source unit) ÷ (factor of target unit)
- factor
- how many metres one unit represents, since the metre is the base unit here
Converting through a common base unit means any pair of units can be converted without a separate formula for each pair.
Worked example
Converting 5 kilometres to miles.
- To metres5 × 1,000 = 5,000 m
- To miles5,000 ÷ 1,609.344
5 km is about 3.1069 miles.
The conversions are exact, not approximate
Since 1959 the inch has been defined as exactly 25.4 millimetres by international agreement, which makes every imperial length unit an exact multiple of a metric one. A foot is exactly 0.3048 m, a mile exactly 1,609.344 m, and a nautical mile exactly 1,852 m.
This calculator uses those exact definitions rather than rounded shortcuts, so converting a value and converting it back returns the original number.
Units that are easy to confuse
A nautical mile is longer than a statute mile and is based on the circumference of the Earth: it was originally one minute of latitude. It is used in aviation and shipping, which is why aircraft speeds are quoted in knots, or nautical miles per hour.
Things to keep in mind
- Very large and very small results switch to scientific notation to stay readable.
- Rounding is applied only for display; the underlying conversion uses full precision.
Frequently asked questions
How many kilometres is one mile?
One mile is exactly 1.609344 kilometres, and one kilometre is about 0.621371 miles.
How many centimetres are in a foot?
Exactly 30.48 centimetres, since a foot is twelve inches and an inch is exactly 2.54 centimetres.
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