What is Length Conversion?
Distance is measured in two families of units: the metric system (millimeters, centimeters, meters, kilometers), used almost everywhere, and the imperial/US system (inches, feet, yards, miles), dominant in the United States and still common in the UK for road distances and human height. Crossing between them — cm to inches for a screen size, km to miles for a run, meters to feet for an apartment listing — is one of the most common conversions there is.
What Does This Tool Do?
Enter a length, choose the source and target units, and get the converted value instantly, plus a table of the same length in all eight supported units at once. The conversions use the exact international definitions (1 inch = 2.54 cm exactly, by treaty since 1959), so results are precise, not approximations.
How to Use This Tool
- Type the length value.
- Pick the unit you’re converting from and to — your choices are remembered.
- Read the result and the full table below it; copy with one click.
- Use ⇄ to flip the direction.
Exact Conversion Factors
| Unit | In meters | Common equivalence |
|---|---|---|
| Millimeter (mm) | 0.001 | 1 in = 25.4 mm |
| Centimeter (cm) | 0.01 | 1 in = 2.54 cm |
| Meter (m) | 1 | 1 m ≈ 3.281 ft |
| Kilometer (km) | 1,000 | 1 km ≈ 0.621 mi |
| Inch (in) | 0.0254 | 1 ft = 12 in |
| Foot (ft) | 0.3048 | 1 yd = 3 ft |
| Yard (yd) | 0.9144 | 1 mi = 1,760 yd |
| Mile (mi) | 1,609.344 | 1 mi ≈ 1.609 km |
Mental Math Shortcuts
- km ↔ miles: multiply km by 0.6 for a quick mile estimate (10 km ≈ 6.2 mi). Curiously, consecutive Fibonacci numbers approximate the ratio: 5 mi ≈ 8 km, 8 mi ≈ 13 km.
- meters → feet: multiply by 3 and add 10% (10 m → 30 + 3 = 33 ft; exact: 32.8).
- cm → inches: divide by 2.5 for a rough figure — then remember the true divisor is 2.54, so shave a bit off.
- Human height: 170 cm = 5′7″, 180 cm = 5′11″, 190 cm = 6′3″ — three anchors that let you interpolate most heights.
Everyday Reference Lengths
| Length | Equals |
|---|---|
| Credit card width | 8.56 cm / 3.37 in |
| A4 paper height | 29.7 cm / 11.7 in |
| Door height | ~2 m / 6′7″ |
| Football (soccer) pitch | ~105 m / 115 yd |
| Running track lap | 400 m / 0.249 mi |
| Marathon | 42.195 km / 26.219 mi |
| Flight cruising altitude | ~11 km / ~36,000 ft |
Popular Conversions
Dedicated pages for the most-searched pairs: cm to inches, inches to cm, km to miles, miles to km, and meters to feet.
Frequently Asked Questions
Is my data private?
Yes — conversions run entirely in your browser, nothing is uploaded, and the tool works offline once the page loads.
Is 1 inch exactly 2.54 cm?
Yes, exactly — since the 1959 international yard and pound agreement, the inch is defined as 25.4 mm. Every imperial length unit derives from that definition, which is why this converter’s factors are exact rather than rounded.
How do I convert height like 5′10″ to centimeters?
Convert the feet and inches separately and add: 5 ft = 152.4 cm, 10 in = 25.4 cm, total 177.8 cm. Or turn it all into inches first (5×12 + 10 = 70 in) and convert once: 70 × 2.54 = 177.8 cm.
What's the difference between a mile and a nautical mile?
The statute mile (1,609.344 m) is a land unit; the nautical mile (1,852 m) is based on one minute of latitude and is used in aviation and shipping. This tool converts statute miles — add roughly 15% to estimate nautical miles.
Why do results sometimes show many decimal places?
Because the factors are exact, the math often produces long decimals (1 m = 3.2808398950… ft). The tool rounds to 8 significant digits — more than enough for any practical use — and you can round further for display.