Length Converter
Free length / distance converter between metric (mm, cm, m, km) and imperial (in, ft, yd, mi) units. Uses the international definitions. Works in your browser.
Pick a “from” unit, a “to” unit, and a value. The calculator converts between any pair of metric and imperial length units.
The conversion factors
All factors are exact by definition since the 1959 international yard- and-pound agreement:
| Unit | Metres |
|---|---|
| 1 mm | 0.001 m |
| 1 cm | 0.01 m |
| 1 m | 1 m |
| 1 km | 1,000 m |
| 1 in | 0.0254 m |
| 1 ft | 0.3048 m |
| 1 yd | 0.9144 m |
| 1 mi | 1,609.344 m |
To convert from unit X to unit Y, multiply value by X’s factor (gets metres), then divide by Y’s factor (gets the target unit).
Statute mile, not nautical
The mile here is the statute mile (1,609.344 m) — what road signs in the US and UK use. The nautical mile (1,852 m exactly) is a different unit, used in aviation and at sea. If you need it, that’s a separate calculator (or just multiply km by 0.5400).
Useful approximate equivalents
For quick estimation without the calculator:
- 1 m ≈ 3.28 ft ≈ 39.37 in
- 1 km ≈ 0.621 mi (or “5 km is about 3.1 miles” — half-marathon math)
- 1 mi ≈ 1.609 km (60 mph ≈ 96.6 km/h)
- 1 in ≈ 2.54 cm (this is exact)
- 1 ft ≈ 30.48 cm (this is exact)
For precision use the calculator. For mental arithmetic these are close enough to surprise people in conversation.
Worked examples
-
1 kilometre in miles
1 km = 0.6213711922 mi
-
100 metres in feet
100 m = 328.0839895013 ft
Frequently asked questions
What conversion factors does this use?
The international definitions: 1 in = 0.0254 m (exact), 1 ft = 0.3048 m (exact), 1 yd = 0.9144 m (exact), 1 mi = 1609.344 m (exact). The metric prefixes are SI: 1 mm = 0.001 m, 1 cm = 0.01 m, 1 km = 1000 m. All conversions go through metres for consistency.
Why are imperial factors \"exact\"?
Since 1959 the international yard and pound have been defined as exact metric values — 1 yd ≡ 0.9144 m. So the foot, inch and mile are exact too. There's still a US survey foot (~0.3048006 m) used in some legacy land-surveying contexts, but for everyday conversion the international foot is what you want.
Mile or nautical mile?
This calculator uses the statute (international) mile, 1,609.344 m — the one used in road signs in the US and UK. The nautical mile is different (1,852 m exactly, used in aviation and maritime navigation).
What about kilometres-per-hour vs. miles-per-hour?
Same factors apply to speeds since speed is just distance/time. 100 km/h = 62.137 mph; 60 mph = 96.561 km/h. We'll add a dedicated speed converter as a separate page.
How precise are the results?
Internal math is full double-precision (about 15 significant digits). The display shows up to 10 fractional digits and strips trailing zeros. For most everyday use that's well beyond meaningful precision — typical tape measure or odometer readings are ±1 mm or ±0.1 mile.
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