How length conversion works
Every length unit is defined as a fixed multiple of the metre. To convert, the tool first turns your number into metres and then divides by the size of the unit you want. For example, one inch is exactly 0.0254 metres, so 100 centimetres (1 metre) equals 1 ÷ 0.0254 = 39.3701 inches. Going the other way, you multiply inches by 2.54 to get centimetres. Because the factors used here are the exact legal definitions rather than rounded approximations, you will not pick up small errors when you chain several conversions together.
The exact definitions behind the factors
- Inch: exactly 2.54 centimetres, fixed by the international yard and pound agreement of 1959.
- Foot: exactly 12 inches, or 0.3048 metres. Yard: exactly 3 feet, or 0.9144 metres.
- Mile: exactly 1,760 yards, or 1,609.344 metres. This is the statute mile used for road distances in the United States and United Kingdom.
- Nautical mile: exactly 1,852 metres, used in sea and air navigation.
Common conversions at a glance
Many people only need a handful of everyday conversions. A height of 170 cm is about 5 feet 7 inches. A 10 km run is about 6.21 miles. A marathon of 42.195 km is about 26.22 miles. A 55-inch television is about 140 cm measured along the diagonal. Rather than memorising factors, type the number and read the answer, then use the table to see the equivalent in other units at the same time.
Tips for accurate results
Check the unit label before you copy a result. Mixing up millimetres and centimetres is the most common mistake in DIY and sewing projects, and it creates a tenfold error. When you convert measurements for building or manufacturing, round only at the very end, and decide how many decimal places the job really needs. Inches are traditionally written as fractions such as 3/8, so divide the decimal part by 0.125 to see the nearest eighth. If a measurement is a sum of feet and inches, convert the feet to inches first (multiply by 12), add the inches, and then convert the total.
Privacy and limits
The conversion runs in your browser and nothing you type is uploaded. Results show up to eight significant digits. Very large or very small values switch to scientific notation. The tool converts lengths only; for speed, weight or volume use the matching converters on this site.