Convert millimeters, centimeters, meters, kilometers, inches, feet, yards and miles — live results as you type.
How length conversion works
Metric length units are decimal multiples of the meter; imperial and US units use fixed historical ratios (12 inches per foot, 1,760 yards per mile). The factor table below shows every unit against the meter, so you can convert by hand — multiply by the source factor, divide by the target factor — or just use the calculator above.
| Unit | Equals |
| 1 Millimeter (mm) | 0.001 m |
| 1 Centimeter (cm) | 0.01 m |
| 1 Meter (m) | base unit |
| 1 Kilometer (km) | 1000 m |
| 1 Inch (in) | 0.0254 m |
| 1 Foot (ft) | 0.3048 m |
| 1 Yard (yd) | 0.9144 m |
| 1 Mile (mi) | 1609.34 m |
All length conversions
Every length pair has its own quick-reference page with a conversion table:
Back to the full unit converter for all seven categories.
Common mistakes to avoid
- Mixing up ounces. The Weight category uses the ounce (oz), a unit of mass (28.3495 g). The Volume category uses the US fluid ounce (fl oz), a unit of capacity (29.5735 mL). One fluid ounce of water weighs about 1.04 oz, not exactly 1 oz, so always confirm which category you are in before converting.
- Confusing bits and bytes. File sizes are measured in bytes, network speeds in bits. In Data storage, 1 byte equals 8 bits, so a 100 Mbit per second connection transfers at most 12.5 megabytes per second.
- Assuming imperial gallons. Every volume unit here is US customary: 1 US gallon is 3.785 liters. A UK imperial gallon is 4.546 liters, roughly 20 percent larger, so results will not match UK fuel economy figures.
A quick accuracy check
Want to sanity-check any converter? Convert -40 from Celsius to Fahrenheit: the result must be exactly -40, the only temperature where the two scales meet. Then convert 0 Kelvin to Celsius: you should get -273.15, absolute zero. A converter that handles both edge cases correctly has sound temperature formulas, and this one does.
Frequently asked questions
How many centimeters are in an inch?
Exactly 2.54 cm. The inch has been defined as exactly 25.4 mm since 1959, so every inch-based conversion here is exact rather than approximate.
What is the difference between metric and imperial length units?
Metric units (mm, cm, m, km) scale by powers of ten, so converting between them only moves the decimal point. Imperial units (inches, feet, yards, miles) use fixed ratios: 12 inches = 1 foot, 3 feet = 1 yard, 1,760 yards = 1 mile.