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A nautical mile (NM) is exactly 1,852 metres, about 6,076 ft or 1.151 statute miles. A knot is one nautical mile per hour. Aviation and shipping use them because a nautical mile is, by origin, one minute of latitude, so distances fit naturally with the latitude and longitude grid on every chart.
Quick conversions
| Nautical miles | Kilometres | Statute miles |
|---|---|---|
| 1 NM | 1.852 km | 1.151 mi |
| 10 NM | 18.52 km | 11.51 mi |
| 60 NM | 111.1 km | 69.05 mi |
| 100 NM | 185.2 km | 115.1 mi |
| 500 NM | 926 km | 575.4 mi |
The same factors work for speed: knots × 1.852 = km/h, and knots × 1.151 = mph. So 120 kt is about 222 km/h or 138 mph. The Nautical Miles Converter does exact conversions.
Where the nautical mile comes from
There are 360 degrees around the Earth and 60 minutes in each degree, so 21,600 minutes in a full circle. A nautical mile was originally the distance along a meridian covered by one minute of latitude. Because the Earth is slightly flattened, that distance varies a little with latitude, so in 1929 the international nautical mile was fixed at exactly 1,852 m. That is why 60 NM is one degree of latitude, anywhere in the world.
Measuring distance on a chart
Because one minute of latitude equals one nautical mile, the latitude scale on the left or right edge of a chart is a ready-made ruler. Set dividers on the two points, then read the distance off the latitude scale beside them.
Never use the longitude scale along the top or bottom. Lines of longitude converge towards the poles, so a degree of longitude shrinks:
| Latitude | 1° of longitude |
|---|---|
| 0° (equator) | 60 NM |
| 25° | about 54 NM |
| 45° | about 42 NM |
| 60° | 30 NM |
The rule is 1° of longitude = 60 NM × cos(latitude).
Why knots make mental arithmetic easy
- Distance per minute: divide ground speed by 60. At 120 kt you cover 2 NM a minute; at 90 kt, 1.5 NM; at 480 kt, 8 NM.
- The 1 in 60 rule: 1° of track error puts you about 1 NM off course after 60 NM. See The 1 in 60 Rule Explained.
- Descent planning: about 3 NM for every 1,000 ft to lose on a 3° path. Try the Descent Rate Calculator.
For full time, speed and distance problems, see the Time, Speed and Distance guide and calculator.
Where aviation does not use nautical miles
- Visibility: statute miles in the United States and Canada (
10SM), metres and kilometres elsewhere (9999). - Runway length: feet or metres depending on the country.
- Wind: knots almost everywhere, but some countries report metres per second (
MPS). 1 m/s is about 1.94 kt. - Altitude: feet in most of the world, metres in a few States. Use the Feet / Metres Converter.
Common mistakes
- Taking a distance from a road map or phone app and treating statute miles or kilometres as nautical miles.
- Measuring on the longitude scale of a chart.
- Mixing km/h and knots in a wind or speed calculation.
- Forgetting that a knot is already a speed. “Knots per hour” is not a unit.
Educational content only. Use approved charts and navigation equipment for flight.
Sources and further reading
- FAA Pilot’s Handbook of Aeronautical Knowledge (FAA-H-8083-25) (navigation chapter)
- FAA Pilot/Controller Glossary
- ICAO Annex 5, Units of Measurement to be Used in Air and Ground Operations
Sources checked November 2026. Rules differ between countries and change over time: for real flights, use the current publications of the authority that applies to you, your aircraft flight manual and your operator’s procedures.