How the length converter works
Enter a value, choose the unit you're converting from and the unit you're converting to, and the result appears instantly. Every unit is converted through the meter, the SI base unit of length, using exact factors, so converting feet to miles gives the same answer as converting feet to meters and then meters to miles.
Exact conversion factors
The meter itself is defined by the speed of light, as set out in the SI Brochure published by the International Bureau of Weights and Measures. All of the imperial units here have been defined in terms of the meter since the 1959 international yard and pound agreement, which fixed the yard at exactly 0.9144 meters (NIST SP 811 lists the official factors). That makes these factors exact, not rounded:
| Unit | Symbol | In meters |
|---|---|---|
| Kilometer | km | 1,000 |
| Meter | m | 1 |
| Centimeter | cm | 0.01 |
| Millimeter | mm | 0.001 |
| Mile | mi | 1,609.344 |
| Yard | yd | 0.9144 |
| Foot | ft | 0.3048 |
| Inch | in | 0.0254 |
Within the imperial system: 1 mile = 1,760 yards = 5,280 feet, 1 yard = 3 feet, and 1 foot = 12 inches.
Quick reference
| From | To | Multiply by |
|---|---|---|
| inches | centimeters | 2.54 |
| centimeters | inches | 0.3937 |
| feet | meters | 0.3048 |
| meters | feet | 3.2808 |
| yards | meters | 0.9144 |
| meters | yards | 1.0936 |
| miles | kilometers | 1.609344 |
| kilometers | miles | 0.6214 |
Worked examples
- A 6-foot person in centimeters: 6 ft × 12 = 72 in, and 72 × 2.54 = 182.88 cm.
- A 10 km run in miles: 10 × 0.6214 = 6.21 miles.
- A marathon in kilometers: 26.2188 miles × 1.609344 = 42.195 km.
- A 55-inch TV screen (diagonal) in centimeters: 55 × 2.54 = 139.7 cm.
Metric vs. imperial
The metric system scales by powers of ten, so converting within it is a matter of moving the decimal point: 1 km = 1,000 m = 100,000 cm. Imperial units use mixed ratios (12 inches to a foot, 3 feet to a yard, 1,760 yards to a mile), which is why conversions within imperial are where most mistakes happen. The United States still uses customary units (feet, inches, miles) in everyday life, and the UK uses metric for most purposes but keeps miles on road signs.
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