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 for Nautical Mile (nmi)
This table quickly gives you the overview you need to understand Nautical Mile (nmi) and its most important comparisons.
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 about Nautical Mile (nmi)
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.
Test your knowledge
Quiz: how well do you know nautical miles?
4 questions · ~2 min
1 / 4
1. What is a nautical mile, and what geometric property makes it essential for navigation?
ℹThe definition states a nautical mile is exactly 1,852 meters, defined as one arcminute (1/60 of a degree) of latitude along any meridian. This geometric relationship to Earth's coordinate system means navigators can read distances directly off the latitude scale on a chart without any conversion.
2. According to the examples table, how many nautical miles correspond to one full degree of latitude?
ℹThe examples table shows 60 nmi = 111.12 km = 69.05 mi labeled as "1 degree of latitude." The definition explains this directly: a nautical mile is one arcminute of latitude, so one degree (60 arcminutes) equals exactly 60 nautical miles.
3. The pitfalls section warns against confusing nautical miles with statute miles. Approximately how much longer is a nautical mile?
ℹThe pitfalls section states a statute mile is 1,609.344 m and a nautical mile is 1,852 m - about 15% longer. It warns that a voyage of "100 miles" could mean very different distances depending on the unit, and that GPS devices must always be verified for the correct setting before navigation.
4. Is the nautical mile part of the SI (metric) system?
ℹThe FAQ states the nautical mile is not part of the SI system. However, its definition of exactly 1,852 m was fixed by international agreement in 1929, and the International System of Units allows its continued use alongside SI units for maritime and aviation purposes.
