Length Converter
Enter a length in any unit and get the equivalent value in all eight others at once, including a feet-and-inches compound display, yards, millimetres and nautical miles. Every conversion uses the exact SI-defined factors, so there is no rounding error in the definitions themselves.
Formula
Worked example
5 ft 10 in = (5 x 12 + 10) in = 70 in x 0.0254 = 1.778 m. Reverse: 1.778 / 0.3048 = 5.833 ft; 0.833 x 12 = 10 in.
How the conversions work
All nine units trace back to one anchor: one inch is defined as exactly 2.54 centimetres, a standard adopted by the US, UK, Canada and Australia in 1959. From that, one foot is exactly 12 inches (0.3048 m), one yard is exactly 3 feet (0.9144 m), one international mile is exactly 5280 feet (1609.344 m), and one nautical mile is exactly 1852 metres (an international standard set in 1929). The calculator converts your input to metres first, then divides by each unit factor to get every result. Because the factors are exact rational numbers, the only source of imprecision is floating-point arithmetic in the processor, which is negligible for any practical length.
The feet-and-inches compound display
Building, tailoring, and body-measurement contexts often write heights as a mixed number such as 5 ft 10 in rather than 5.833 ft or 70 in. The compound display splits the decimal feet result into a whole-feet part and a remaining-inches part: whole feet = floor(total inches / 12), remaining inches = total inches mod 12. For example, 1.80 m is 70.866 in, which is 5 ft 10.87 in. The inches remainder is rounded to two decimal places; the feet are always a whole number. This output is labelled "Feet and inches" in the results grid.
Nautical miles and why they differ
A nautical mile (nmi) is exactly 1852 metres, defined so that one nautical mile equals one arc-minute of latitude on the Earth surface. This makes navigation arithmetic clean: one degree of latitude = 60 nmi. A nautical mile is about 15% longer than a land mile (1852 m vs 1609.344 m). Knots, the speed unit used in aviation and maritime navigation, measure nautical miles per hour. If you are converting from a speed in knots to km/h, multiply by 1.852.
Metric prefixes and the metre family
The metre is the SI base unit of length. Its named multiples cover the practical range: a millimetre (mm) is 0.001 m and is used for fine engineering tolerances; a centimetre (cm) is 0.01 m and is the everyday unit for body measurements in most countries; a kilometre (km) is 1000 m and is used for road distances and geography. All three are exact powers of ten, so metric-to-metric conversions never involve any approximation at all.
Which units to use when
Metres and centimetres suit everyday indoor and body measurements. Kilometres and miles suit road distances: use km in most of the world, miles in the US and UK. Millimetres are standard in engineering, woodworking and printing. Yards appear in American football field markings, golf distances and US fabric sales. Nautical miles are used in aviation and maritime navigation. Feet and inches remain common for human height in the US and UK. The conversion table below gives the exact factor between every pair of the nine units this calculator supports.
Length unit conversion factors (to metres)
| Unit | Symbol | Metres (exact) | Practical note |
|---|---|---|---|
| Millimetre | mm | 0.001 | Engineering tolerances, thread pitch |
| Centimetre | cm | 0.01 | Body measurements, everyday metric |
| Metre | m | 1 | SI base unit of length |
| Kilometre | km | 1000 | Road distances in most of the world |
| Inch | in | 0.0254 | US/UK small measurements, screen sizes |
| Foot | ft | 0.3048 | US/UK height, construction |
| Yard | yd | 0.9144 | US football, golf, fabric |
| Mile | mi | 1609.344 | US/UK road distances |
| Nautical mile | nmi | 1852 | Aviation, maritime (= 1 arc-min latitude) |
Multiply the value in column A by the factor shown to get metres. All factors are exact by international definition except where noted.
Frequently asked questions
How many centimetres are in an inch?
One inch is exactly 2.54 centimetres by international definition, adopted jointly by the US, UK, Canada, and other countries in 1959. This is not an approximation: there is no rounding involved in the definition itself.
What is the difference between a mile and a kilometre?
One international mile equals exactly 1609.344 metres, or about 1.609 kilometres. One kilometre is about 0.6214 miles. Road signs in the UK use miles; most of the rest of the world uses kilometres.
How many feet are in a metre?
One metre equals exactly 1/0.3048 feet, which is approximately 3.28084 ft. For quick mental arithmetic, 3.28 feet per metre is accurate to within 0.003%.
How do I convert metres to feet and inches?
Divide the metres by 0.3048 to get total decimal feet, then multiply the fractional part by 12 to get inches. For example, 1.75 m / 0.3048 = 5.7415 ft; the whole part is 5 ft and 0.7415 x 12 = 8.90 in, so 1.75 m = 5 ft 8.90 in. The calculator does this automatically in the "Feet and inches" output.
How many yards are in a mile?
Exactly 1760 yards in one international mile. One yard is exactly 0.9144 m, and one mile is exactly 1609.344 m; dividing gives 1609.344 / 0.9144 = 1760 exactly.
What is a nautical mile in kilometres?
One nautical mile is exactly 1852 metres, or 1.852 kilometres. It is longer than a land mile (1609.344 m). The nautical mile is defined as one arc-minute of latitude, which is why navigators use it: one degree of latitude equals exactly 60 nautical miles.
Why does the calculator say the US survey foot was retired?
The US survey foot (0.304800609601 m) differed from the international foot (0.3048 m exactly) by about two parts per million. NIST officially retired the US survey foot on 1 January 2023. This calculator uses the international foot, which is the current legal standard.