Length Converter
Nine Units, One Common Reference
Length is the most-converted quantity there is, and also the one where the two dominant systems refuse to line up. The metre is defined by the speed of light; the inch is defined as exactly 0.0254 metres by international agreement, and every other imperial length — foot, yard, mile — is derived from that one anchor. Because the inch was pinned to an exact decimal in 1959, every conversion on this page is exact rather than approximate, which is why the numbers below terminate cleanly instead of trailing off.
The Formula
This converter does not carry 72 separate conversion pairs. It stores a single factor per unit — how many metres that unit is worth — and routes every conversion through the metre as a pivot:
(Factors are relative to 1 meter)
Converting 5 miles to feet, for instance, evaluates as 5 × 1609.344 ÷ 0.3048 = 26,400 feet. The pivot approach means the same nine factors handle all 81 possible unit pairings with no rounding introduced at an intermediate step.
The Factor Table This Calculator Uses
These are the exact values in the converter's unit table. Every one is a defined constant, not a measurement:
| Unit | Code | Metres per unit |
|---|---|---|
| Millimeters | mm | 0.001 |
| Centimeters | cm | 0.01 |
| Meters | m | 1 |
| Kilometers | km | 1000 |
| Inches | in | 0.0254 |
| Feet | ft | 0.3048 |
| Yards | yd | 0.9144 |
| Miles | mi | 1609.344 |
| Nautical Miles | nmi | 1852 |
The nautical mile is the odd one out: it is defined as exactly 1852 metres, chosen to approximate one minute of latitude, and is not derived from the inch.
Full Conversion Reference
One of each unit, expressed in the four units people most often need:
| 1 of… | Meters | Centimeters | Inches | Feet |
|---|---|---|---|---|
| Millimeter | 0.001 | 0.1 | 0.03937008 | 0.00328084 |
| Centimeter | 0.01 | 1 | 0.39370079 | 0.0328084 |
| Meter | 1 | 100 | 39.37007874 | 3.2808399 |
| Kilometer | 1000 | 100000 | 39370.07874 | 3280.8399 |
| Inch | 0.0254 | 2.54 | 1 | 0.08333333 |
| Foot | 0.3048 | 30.48 | 12 | 1 |
| Yard | 0.9144 | 91.44 | 36 | 3 |
| Mile | 1609.344 | 160934.4 | 63360 | 5280 |
| Nautical Mile | 1852 | 185200 | 72913.38583 | 6076.11549 |
Kilometres to Miles at a Glance
| Kilometers | Miles |
|---|---|
| 1 km | 0.62137119 mi |
| 5 km | 3.10685596 mi |
| 10 km | 6.21371192 mi |
| 20 km | 12.42742384 mi |
| 42.195 km (marathon) | 26.21875746 mi |
| 50 km | 31.06855961 mi |
| 100 km | 62.13711922 mi |
Where Precision Actually Bites
- Machining and fabrication — a drawing dimensioned in inches cut on a metric machine needs the exact 25.4 mm/inch factor, not the 25 mm approximation. Over a 36-inch part the shortcut is off by more than 14 mm.
- Marine and aviation navigation — distances are quoted in nautical miles, altitudes in feet, and chart scales in metres. Mixing the two mile definitions (1852 m vs 1609.344 m) is a 15% error.
- Construction takeoffs — imperial plans priced against metric material stock (sheet goods, timber, rebar) require converting every dimension before ordering.
- Race distances and pacing — converting a metric race distance to miles is the first step in setting a per-mile target pace.
How to Use This Calculator
- Type the number you want to convert into the Value field — decimals are accepted.
- Pick the unit that number is currently in from the first dropdown (the from unit).
- Pick the unit you want in the second dropdown (the to unit).
- Press Calculate. The result appears with the full arithmetic shown, including the two factors used, so you can verify the step.
Related Calculations
Squaring the problem? The Area Converter handles square metres, feet and acres. For distance covered over time, see the Speed Converter.