This free length converter changes nautical miles (nmi) into kilometers (km) and back again. A nautical mile is the distance unit used in maritime and air navigation, while the kilometre is the everyday metric unit — this tool bridges the two for sailors, pilots, students and anyone reading a chart.
How it works
The conversion uses a single exact factor. Since 1929 the international nautical mile has been defined as precisely 1852 metres, so:
- km = nmi × 1.852
- nmi = km ÷ 1.852
Type a value in either field and the other updates in real time, using whichever field you last edited as the source.
Examples
To convert 10 nautical miles to kilometres, multiply by 1.852:
10 × 1.852 = 18.52 km
To go the other way, 50 km in nautical miles is 50 ÷ 1.852 ≈ 26.998 nmi.
| Nautical Miles (nmi) | Kilometers (km) |
|---|---|
| 1 nmi | 1.852 km |
| 5 nmi | 9.26 km |
| 10 nmi | 18.52 km |
| 50 nmi | 92.6 km |
| 100 nmi | 185.2 km |
| 200 nmi | 370.4 km |
| 500 nmi | 926 km |
Why nautical miles exist
The nautical mile was originally defined as one minute of arc of latitude along a meridian of the Earth. Because one degree of latitude equals 60 nautical miles, a chart graduated in nautical miles doubles as a latitude scale — you can measure distance directly with dividers against the latitude margin. This geometric elegance made the unit indispensable for navigation long before GPS.
The kilometre, by contrast, was originally defined as one ten-thousandth of the distance from the equator to the North Pole — a metric convenience but one that does not map neatly onto angular measurement. That is why aviation and maritime navigation kept their own unit even after metrication.
Where you encounter nautical miles
- Aviation: aircraft speeds are given in knots (nautical miles per hour), and flight-plan distances appear in nautical miles on charts and FMS systems.
- Maritime: ship speeds, voyage distances, and admiralty charts all use nautical miles. A passage from the UK to the Canary Islands is roughly 1,500 nmi.
- Weather and oceanography: storm tracks, buoy positions, and search-and-rescue radii are cited in nautical miles.
- Fishing and exclusive economic zones: EEZ boundaries are defined in nautical miles under international law (typically 200 nmi from the baseline).
Common conversion mistakes
The most frequent error is confusing a nautical mile with a statute (land) mile. A statute mile is about 1,609 metres, a nautical mile is 1,852 metres — the nautical mile is roughly 15% longer. Using the wrong conversion would misplace a 100 nmi position by nearly 25 km.
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