Free Length Converter
Convert length units instantly — meters, feet, inches, miles, kilometers, and more. Type into any field and all others update. Free, symmetrical, no sign-up.
Exact Conversion Formula & Multipliers
The metric-imperial bridge for length runs through three internationally defined constants: 1 inch = 2.54 centimeters (exact, agreed in 1959), 1 foot = 0.3048 meters (exact, since it equals 12 inches), and 1 mile = 1.609344 kilometers (exact, derived from 5,280 feet). Every other length conversion on this page — yards, nautical miles, microns — is built from these three fixed multipliers, so results are never approximations layered on approximations.
Practical Real-World Scenarios
- Engineering and manufacturing: machinists convert between millimeters and thousandths of an inch when a CAD drawing from a metric supplier meets an imperial tolerance spec.
- International travel: road signs switch from kilometers to miles at borders like the US-Canada crossing, so drivers convert speed and distance on the fly.
- Construction and aviation: runway lengths and cloud ceilings are published in feet even in metric countries, while land surveys use meters — both appear on the same site plan.
Historical & Technical Background
The imperial system's foot and inch trace back to Anglo-Saxon body-based measures standardized piecemeal over centuries, while the metric meter was defined in 1799 as one ten-millionth of the distance from the equator to the North Pole. Since 1983 the meter has been redefined via the speed of light, making it independent of any physical artifact. NIST lists the United States, Liberia and Myanmar as the only countries without a mandatory metric law; Liberia and Myanmar have announced metrication, and in daily life the US is the main country using US customary units — which is why converters like this one remain practical rather than a historical curiosity.
Precision & Accuracy Statement
Conversion factors use the exact defined values given in NIST Special Publication 811 and the BIPM SI Brochure wherever such a definition exists (for example 1 lb = 0.45359237 kg, 1 in = 2.54 cm, 1 US gal = 3.785411784 L, g₀ = 9.80665 m/s²); derived factors are computed from those definitions rather than copied as rounded figures. Results are calculated in double-precision floating point and shown to 10 significant digits, so the last digit can differ by one unit of rounding. The rounded figures in the text and tables above are for reading convenience. The light year uses the IAU definition (Julian year × speed of light = 9,460,730,472,580,800 m).
How This Converter Works
Length is measured differently across metric and imperial systems. Meters dominate science and most of the world, while feet and inches remain common in the US and UK. Our converter handles 12 units simultaneously.
Common Conversions
| Meters (m) | Feet (ft) | Inches (in) | Context |
|---|---|---|---|
| 0.0254 m | 0.083 ft | 1 in | One inch |
| 0.3048 m | 1 ft | 12 in | One foot |
| 1 m | 3.281 ft | 39.37 in | One meter |
| 1.8288 m | 6 ft | 72 in | Tall person's height |
| 100 m | 328.1 ft | 3,937 in | Olympic sprint distance |
| 1,609.34 m | 5,280 ft | 63,360 in | One mile |