Nautical Mile (nmi)
→ Use the Nautical Mile (nmi) CalculatorWhat is Nautical Mile (nmi)?
A nautical mile is a unit of distance equal to exactly 1,852 meters (1.852 km or approximately 1.151 statute miles). It is defined as one arcminute (1/60 of a degree) of latitude along any meridian of Earth's surface. This geometric relationship to Earth's coordinate system is what makes it essential for navigation.
Because one degree of latitude = 60 nautical miles, navigators can read distances directly off the latitude scale on a chart using a compass or dividers - no conversion required. A ship travelling 1 nautical mile has moved exactly 1 arcminute of latitude toward the equator or poles.
When to use Nautical Mile (nmi)
Use nautical miles for any oceanic or aviation navigation - measuring distances on charts, filing flight plans, calculating fuel range, and setting waypoints. Combine with knots to express speed: a ship travelling at 20 knots covers 20 nautical miles per hour. For road or land distances, use kilometres or statute miles instead.
Worked examples
| Nautical miles | Kilometres | Statute miles | Context |
|---|---|---|---|
| 1 nmi | 1.852 km | 1.151 mi | Definition |
| 60 nmi | 111.12 km | 69.05 mi | 1 degree of latitude |
| 3,600 nmi | 6,667.2 km | 4,143 mi | Paris to New York (approx.) |
| 21,600 nmi | 40,003.2 km | 24,860 mi | Earth's circumference (approx.) |
Common pitfalls
Do not confuse nautical miles with statute miles. A statute mile is 1,609.344 m; a nautical mile is 1,852 m - about 15% longer. A voyage of "100 miles" could mean very different distances depending on which unit is used. GPS devices typically allow switching between nmi and statute miles - always verify the setting before navigation.
Frequently asked questions
Why is it called a "nautical" mile?
The term distinguishes it from the statute mile (used on land). "Nautical" simply means relating to the sea or navigation. Before GPS, sailors needed a distance unit directly readable from latitude lines on a chart - the nautical mile, defined as one arcminute of latitude, fulfilled this exactly.
Is the nautical mile metric?
Not officially - it is not part of the SI system. However, its definition (1,852 m exactly) was fixed by international agreement in 1929, making it a precisely defined unit with an exact metric equivalent. The International System of Units allows its continued use alongside SI units for maritime and aviation purposes.