Length Converter Free Online
Convert between metric and imperial length units instantly. Supports meters, kilometers, centimeters, millimeters, micrometers, inches, feet, yards, miles, and nautical miles. Bidirectional conversion with live updates as you type.
All Conversions
Pro — bulk batch conversion, API access, history & favorites
API access · Priority queue · Team workspace
How It Works
Enter a Value
Type the number you want to convert into the From input. The conversion runs as you type — there is no Convert button. Numbers can be integers or decimals (with a dot or comma) and you can paste long values directly. The tool handles very small numbers (micrometer scale) and very large numbers (planetary distances) without losing precision.
Pick Source & Target Units
Use the two dropdowns to choose the source unit (From) and the destination unit (To). The result updates automatically. Use the swap button between the two panels to flip the conversion direction with a single click — useful for verifying that a conversion round-trips cleanly.
See All Conversions
Below the main result, the All Conversions panel shows your input value converted into every supported unit at once. This is useful when you do not yet know which target unit you need, or when you want to compare metric vs imperial equivalents side by side.
Length Converter Features
Metric Units
Full SI metric coverage: millimeter, centimeter, meter, kilometer, micrometer. All conversions go through meters as the base unit, so multi-step conversions (e.g. micrometer → kilometer) stay numerically accurate without intermediate rounding errors.
Imperial / US Units
Inch, foot, yard, mile — the standard US customary and UK imperial length units. Uses internationally agreed conversion factors (1 inch = exactly 25.4 mm, 1 mile = exactly 1609.344 m) so results match those used by NIST and BIPM.
Nautical Mile
The nautical mile (1852 m exactly) is the standard unit for marine and aviation navigation, equal to one minute of latitude. Useful for converting between flight charts (NM) and metric maps (km), or for marine speed (knots → km/h).
Live Conversion
Conversion runs on every keystroke. No need to press Enter or click Convert. The result and the All Conversions panel both update in real time, so you can hold a key or paste a value and see the conversion immediately.
One-Click Swap
The circular swap button flips the From and To units (and the values) instantly. This is much faster than re-selecting both dropdowns when you realize you need the inverse conversion, and it lets you check round-trip accuracy.
100% Private
All conversion math runs locally in your browser using JavaScript. Nothing is sent to a server, no analytics tracks the values you enter. Safe for engineering, scientific, or commercial measurements that you do not want exposed to third-party tools.
Free vs Pro
| Feature | Free | Pro |
|---|---|---|
| All 10 length units | ||
| Live conversion | ||
| All-units result table | ||
| Bulk CSV / Excel conversion | — | |
| REST API access | — | |
| Custom precision settings | — |
Frequently Asked Questions
All conversion factors are taken from the international SI definition. 1 inch = exactly 25.4 mm, 1 yard = 0.9144 m, 1 mile = 1609.344 m, 1 nautical mile = 1852 m. JavaScript double-precision floats give about 15 significant digits, so the result is accurate well beyond what you need for engineering, construction, or navigation work. Display rounds to 6 significant digits to keep results readable.
Micrometer (μm = 0.000001 m) covers the scale of microscopy, microelectronics, and biology. For nanometer (1e-9 m) or angstrom (1e-10 m) scales used in chemistry and crystallography, divide a micrometer value by 1000 or 10000 respectively. We may add nanometer in a future update if there is demand.
Yes — enter the value in inches and pick meters as the target. To convert a height like 5 ft 9 in, multiply 5 by 12 = 60, add 9 = 69 inches, then convert 69 in to meters (1.7526 m). A combined feet+inches input field is on the roadmap.
Yes. Once the page is loaded, all conversion math runs in your browser without any further network requests. You can disconnect and the tool keeps working. Open the page once on a flight or in a remote location, leave the tab open, and conversions stay available.
Length units (inch, foot, yard, mile) are identical in US customary and UK imperial systems — both use the same International Yard and Pound agreement values from 1959. The differences are only in volume (US gallon ≠ UK gallon) and weight (US ton ≠ UK ton). Use our weight and volume converters for those.