Units
What Is a Nautical Mile? Why Sailors Use It
Published · Last checked October 2026
A nautical mile is 1,852 metres, about 6,076 feet or 1.15 statute miles. It is used at sea and in the air because it equals one minute of latitude, so distances can be measured straight off the side of a chart. Speed at sea is measured in knots: one knot is one nautical mile per hour.
Why one minute of latitude
The Earth is divided into 360 degrees, and each degree into 60 minutes. Measured along a meridian, one minute of arc at the Earth's surface is roughly one nautical mile. That link lets navigators read distance from a chart's latitude scale using dividers. The actual length of a minute varies slightly because the Earth is not a perfect sphere, so the international nautical mile was fixed at exactly 1,852 metres in 1929.
Nautical mile compared with other units
| Unit | Equivalent |
|---|---|
| 1 nautical mile | 1,852 m (exact) |
| 1 nautical mile | about 1.151 statute miles |
| 1 nautical mile | about 6,076 feet |
| 1 cable | 0.1 nautical mile, about 185 m |
| 1 degree of latitude | 60 nautical miles |
Where you meet nautical miles
- Distances on charts, in pilot books and almanacs.
- Ranges of lights and VHF radio coverage.
- Boat speed in knots.
- Territorial waters (12 nautical miles) and other legal limits.
- RYA course requirements, such as miles logged for Yachtmaster.
Cables and shorter distances
Close in, sailors often use cables: a tenth of a nautical mile. 'Pass 2 cables off the headland' means about 370 metres. Depths and heights on modern charts are in metres, so it is worth getting used to both systems. Learn more in the charts and compass lesson.