Nautical miles (nmi)

What is a nautical mile?

The nautical mile is a unit of distance used at sea and in the air, equal to exactly 1,852 meters, or about 1.151 statute miles. It is based on the Earth's shape: one nautical mile is approximately one minute of arc of latitude, so navigators can measure distances directly on a chart's latitude scale.

A speed of one nautical mile per hour is one knot.

What nautical miles are used for

• Marine and aviation navigation
• Territorial waters (12 nmi) and exclusive economic zones (200 nmi)
• Flight distances and air traffic control

Nautical miles in real life

• The English Channel at its narrowest is about 18 nmi wide
• A country's territorial sea extends 12 nautical miles (22.2 km) from shore
• One degree of latitude is about 60 nautical miles

One nautical mile is about 5.6 Eiffel Towers laid end to end, or about 2.2 Burj Khalifas laid end to end, or about 17 American football fields laid end to end, or about 1.4 Golden Gate Bridge spans laid end to end.

History of the nautical mile

Sailors used the minute of latitude as a unit for centuries, but its exact length varied with latitude and between countries. The International Hydrographic Conference fixed it at 1,852 m in 1929; the US adopted this value in 1954 and the UK in 1970.