An exact length converter for every unit you meet
This length converter turns a measurement into every common unit of length at the same time — millimetres, centimetres, metres and kilometres, inches, feet, yards and miles, plus nautical miles, mils, hands, chains, furlongs, fathoms and the astronomical units used for space. Type a value, choose the unit you have and the unit you want, and the answer appears instantly with the exact formula behind it.
It is made for real jobs: checking a TV or laptop screen size in centimetres, turning a room plan from feet into metres for a flooring quote, converting a 10 km race into miles, or reading a drawing in millimetres when your tape measure only shows inches. Every factor comes from an official definition, and results come without the 2.5399999 rounding noise that many calculators produce.
How to use the Length Converter
- Type a number in the Value box. Decimals, fractions such as 5/8 or 1 1/2, and scientific notation such as 3e8 all work.
- Tap From and choose the unit you are starting with. Type in the search box — “ft”, “nautical” or “micron” — to jump straight to it.
- Choose the unit you want in To. The round swap button between the two reverses the conversion.
- Read the big result, the sentence underneath it and the formula, for example
cm = in × 2.54. Change Precision to show between 4 and 15 significant digits, and press Copy to paste the number elsewhere. - Scroll down to see your value in every length unit at once, and tap any row to make it the target unit.
Length Converter features
Exact international definitions
1 inch = 2.54 cm, 1 foot = 0.3048 m, 1 yard = 0.9144 m and 1 mile = 1,609.344 m — the same factors national measurement institutes use, so results never drift.
Twenty units in one view
The “every length unit” list shows your value in metric, imperial, nautical and astronomical units side by side.
Searchable unit lists
Find a unit by name, symbol or nickname — “thou”, “micron”, “NM”, “gaj” — instead of scrolling through a long dropdown.
No floating-point noise
Results are rounded to the significant digits you choose, and very large or very small values switch to scientific notation such as 6.2137 × 10⁻⁷ mi.
Formula for every pair
Each conversion shows the multiplication or division used, so you can check it or repeat it on paper.
Remembers your units
The last pair of units you used is saved on this device, so the converter opens the way you left it.
Exact length conversion factors
Under the International Yard and Pound Agreement of 1959, the yard was fixed at exactly 0.9144 metres. The inch, foot and mile are defined from the yard, which is why the factors below are exact rather than rounded. The metre itself has been defined since 1983 as the distance light travels in a vacuum in 1/299,792,458 of a second.
| Unit | Symbol | Value in metres | Defined as |
|---|---|---|---|
| Inch | in | 0.0254 (exact) | 1/36 of a yard |
| Foot | ft | 0.3048 (exact) | 12 inches |
| Yard | yd | 0.9144 (exact) | 3 feet |
| Mile | mi | 1,609.344 (exact) | 1,760 yards or 5,280 feet |
| Nautical mile | NM | 1,852 (exact) | International definition, adopted 1929 |
| Mil (thou) | mil | 0.0000254 (exact) | 1/1000 of an inch |
| Hand | hh | 0.1016 (exact) | 4 inches — used for horse heights |
| Chain | ch | 20.1168 (exact) | 22 yards (66 feet), the length of a cricket pitch |
| Furlong | fur | 201.168 (exact) | 10 chains or 220 yards |
| Fathom | ftm | 1.8288 (exact) | 6 feet — water depth |
| Ångström | Å | 0.0000000001 | 0.1 nanometre — atomic scales |
| Astronomical unit | au | 149,597,870,700 (exact) | Fixed by the IAU in 2012 |
| Light-year | ly | 9,460,730,472,580,800 | Distance light travels in 365.25 days |
| Parsec | pc | ≈ 3.0857 × 10¹⁶ | 648,000/π astronomical units |
Worked examples
Inches to centimetres — multiply by 2.54. A 15.6-inch laptop screen measures 15.6 × 2.54 = 39.624 cm across the diagonal.
Centimetres to inches — divide by 2.54. A 30 cm ruler is 30 ÷ 2.54 = 11.811 inches, just short of one foot.
Feet to metres — multiply by 0.3048. A 12 ft × 10 ft bedroom is 3.6576 m × 3.048 m, which is 11.148 m² of floor. The area converter does square feet to square metres directly.
Kilometres to miles — divide by 1.609344. A 10 km race is 6.2137 miles, and a marathon of 42.195 km is 26.2188 miles.
Feet and inches to centimetres — go through inches first. 5 ft 9 in is 5 × 12 + 9 = 69 inches, and 69 × 2.54 = 175.26 cm. For heights, the height converter does this in one step.
Common length conversions
Values are shown to 10 significant digits. Conversions such as 1 inch = 2.54 cm are exact; others, such as 1 km = 0.6213711922 mi, are rounded.
| From | To |
|---|---|
| 1 in | 2.54 cm |
| 1 ft | 30.48 cm |
| 1 ft | 0.3048 m |
| 1 yd | 0.9144 m |
| 1 m | 3.280839895 ft |
| 1 m | 39.37007874 in |
| 1 mm | 0.03937007874 in |
| 1 km | 0.6213711922 mi |
| 1 mi | 1.609344 km |
| 1 NM | 1.150779448 mi |
| 100 m | 109.3613298 yd |
| 1 au | 149,597,870.7 km |
Tips for measuring and converting length
- Choose the unit before you measure. Builders often work entirely in millimetres (2,440 mm rather than 2.44 m) to avoid decimal points on drawings.
- Know your local habits. The UK signs roads in miles and yards but sells timber in millimetres; India is officially metric, yet heights and room sizes are still widely quoted in feet and inches; the US uses customary units for almost everything outside science and medicine.
- A nautical mile is not a long statute mile. It is 1,852 m (about 1.1508 miles), chosen because it is close to one minute of latitude. Ships and aircraft pair it with the knot — see the speed converter.
- The US survey foot is retired. It was 1200/3937 m, about two parts per million longer than the international foot, and was officially phased out at the end of 2022. Modern work uses 0.3048 m.
- Round once, at the end. Converting a rounded result back and forth (2.54 → 1 → 2.5) builds up error. Keep full precision until the final figure, then round to what your measurement justifies.
Length Converter FAQ
How many centimetres are in an inch?
Exactly 2.54 cm. The inch has been defined as 25.4 mm by international agreement since 1959, so multiply inches by 2.54 to get centimetres, or divide centimetres by 2.54 to get inches.
How do I convert feet to metres?
Multiply the number of feet by 0.3048. For example, 10 ft × 0.3048 = 3.048 m. To go from metres to feet, divide by 0.3048, which is the same as multiplying by about 3.28084.
How many miles are in a kilometre?
One kilometre is about 0.621371 miles, and one mile is exactly 1.609344 km. For a quick estimate, multiply kilometres by 0.6 or miles by 1.6, then use the length converter for the exact figure.
What is the difference between a mile and a nautical mile?
A statute mile is 5,280 feet, or 1,609.344 m. A nautical mile is 1,852 m — about 1.1508 statute miles — and is used at sea and in aviation because it closely matches one minute of latitude.
Why do some calculators show 2.5399999 instead of 2.54?
Computers store numbers in binary, which cannot represent decimals such as 0.01 exactly, so raw arithmetic leaves tiny errors. This converter rounds to the number of significant digits you choose, so you see 2.54 rather than 2.5399999999999996.
Is this length converter accurate enough for engineering work?
Yes. It uses exact definitions and double-precision arithmetic and can show up to 15 significant digits — but the answer is only as precise as the measurement you enter.