Length Converter
Convert a length between metric units (kilometres to nanometres), US and imperial units (miles, yards, feet, inches) and nautical miles. The factors are the exact legal definitions, and the table shows your value in every unit at once.
Result
Enter a value to convert.
The calculation runs in this browser tab. Nothing you enter is uploaded, saved or logged.
How are units of length defined?
The metre is the base unit of length in the International System of Units (SI). Since 1983 it has been defined from the speed of light: the distance light travels in a vacuum in 1/299,792,458 of a second. Every metric unit is a power of ten of the metre, which is why converting between kilometres, metres, centimetres and millimetres only moves the decimal point.
The inch, foot, yard and mile are defined in terms of the metre. Under the international yard and pound agreement of 1959, one yard is exactly 0.9144 metre, so one inch is exactly 25.4 millimetres, one foot exactly 0.3048 metre and one statute mile exactly 1,609.344 metres. The nautical mile is exactly 1,852 metres, close to one minute of latitude.
How to use the Length Converter
- Enter the length you want to convert. Decimals and negative values (a displacement, for example) are accepted.
- Choose the unit you are converting from and the unit you are converting to.
- Read the result at the top, together with the conversion factor and its inverse. A leading ≈ means the exact value was rounded to the precision selected.
- Scroll to the table to see the same value in every unit. Use Copy result to copy the number alone.
Formula
- General rule
- result = value × (metres per source unit) ÷ (metres per target unit)
- Miles to kilometres
- km = mi × 1.609344
- Feet to metres
- m = ft × 0.3048
- Inches to centimetres
- cm = in × 2.54
Each unit is stored as an exact number of metres, so converting a value to another unit and back returns the starting value exactly, with no accumulated rounding.
Handy equivalents: 1 mile = 1,760 yards = 5,280 feet = 63,360 inches; 1 yard = 3 feet; 1 foot = 12 inches.
Worked example
The marathon distance, 26 miles 385 yards (26.21875 miles), converted to kilometres. These are the results the converter gives:
| Question | Result |
|---|---|
| Input: Value | 26.21875 |
| Input: From | Miles (mi) |
| Input: To | Kilometres (km) |
| Input: Precision | 10 significant digits |
| 26.21875 mi equals | 42.194988 km |
| Conversion factor | 1 mi = 1.609344 km |
| Inverse | 1 km = ≈ 0.6213711922 mi |
| Formula | km = mi × 1.609344 |
Assumptions and limits
- The foot used here is the international foot (0.3048 m exactly). The US survey foot, which the United States retired on 1 January 2023, is about two parts per million longer; the difference only matters over very long distances, such as in land surveying.
- Results are shown to 6 to 15 significant digits, as selected. Conversions that do not terminate, like inches to miles, are rounded and marked ≈.
- Inputs can have up to 30 digits. Use a dot for decimals and no thousands separators.
- Only the units listed are offered. Other historical units, such as the league or the fathom, vary by country and period and are not included.
Frequently asked questions
How many kilometres are in a mile?
One mile is exactly 1.609344 kilometres. To convert miles to kilometres, multiply by 1.609344; for a quick estimate, multiply by 1.6.
How many centimetres are in an inch?
Exactly 2.54, because one inch is defined as 25.4 millimetres. So 12 inches (one foot) is 30.48 centimetres.
How do I convert feet and inches to centimetres?
Convert the feet to inches (multiply by 12), add the inches, then multiply the total by 2.54. A height of 5 ft 9 in is 69 inches, which is 175.26 cm.
What is the difference between a mile and a nautical mile?
A statute mile is 1,609.344 m; a nautical mile is 1,852 m, about 15% longer. The nautical mile is used at sea and in aviation, and a speed of one knot is one nautical mile per hour.
How many feet are in a metre?
One metre is about 3.28084 feet (3.280839895… exactly). The reverse is exact: one foot is 0.3048 metre.
Why does the result sometimes have ≈ in front of it?
Some conversions have a result that never ends in decimals, for example 1 metre in feet. The converter rounds those to the precision you selected and marks them with ≈. Exact results such as 1 mile = 5,280 feet have no mark.