Nautical Mile (nmi)

Use the Nautical Mile (nmi) Calculator → Try the Nautical Mile (nmi) Quiz →

What 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.

Nautical Mile (nmi) explained to a beginner

A nautical mile is longer than a regular (statute) mile: 1,852 meters versus 1,609 meters - about 15% longer. On a map, it is the distance you travel when you move one arcminute (one sixtieth of a degree) up or down a line of longitude.

The practical value is elegance: on any nautical chart, the latitude scale on the side is your ruler. Place a compass at one degree of latitude and spread it: that span is exactly 60 nautical miles. Ancient navigators could measure ocean distances with no calculator, just dividers on a chart. That convenience is why the unit still dominates global aviation and shipping despite the metric system.

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 kilometers 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.

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?

A A nautical mile is exactly 1,000 meters, equivalent to one kilometer, defined by the International Hydrographic Organization as the standard unit for all maritime distance measurements B A nautical mile equals 1,609.344 meters - the same as a statute mile - but named differently to indicate its use in maritime contexts versus land-based travel C A nautical mile is exactly 1,852 meters, defined as one arcminute of latitude along any meridian of Earth's surface - a geometric link to the coordinate system that lets navigators read distances directly off latitude lines on a chart D A nautical mile is approximately 1,852 meters but varies slightly by latitude because Earth is not a perfect sphere, requiring GPS correction factors at extreme latitudes

ℹ The 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?

A 60 nautical miles - because a nautical mile is defined as one arcminute (1/60 of a degree) of latitude, so one full degree equals exactly 60 nautical miles B 100 nautical miles - the metric-aligned rounding used when dividing the globe's 6,000-nautical-mile circumference into 60 equal segments C 69.05 nautical miles - derived from the statute mile equivalent of one degree of latitude at the equator, used in US government navigation tables D 111.12 nautical miles - based on the kilometer conversion, since one degree at the equator spans approximately 111.12 km

ℹ The 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?

A About 5% longer - a small difference that only matters for very long ocean voyages where cumulative error builds across multiple waypoints B About 10% longer - which is why GPS charts flag the discrepancy when users switch between statute and nautical mile settings C They are the same physical distance measured differently; the values 1,852m and 1,609.344m refer to two different calculation methods for the same unit D About 15% longer - a nautical mile is 1,852 m versus a statute mile's 1,609.344 m, so a "100-mile voyage" means very different distances depending on which unit was intended

ℹ The 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?

A Yes - it is a derived SI unit officially adopted by the International Bureau of Weights and Measures when its metric equivalent of 1,852 m was formally established in 1929 B No - it is not part of the SI system, but its exact metric definition (1,852 m) was fixed by international agreement in 1929, and the International System of Units allows its continued use alongside SI for maritime and aviation purposes C No - the nautical mile has no fixed metric equivalent and varies by country; European authorities use 1,852 m while the US still uses the traditional 1,853.248 m derived from Clarke's ellipsoid D Yes - the nautical mile was fully metricated in 1960 when the SI system was formally adopted, classified as a supplementary unit for approved navigation contexts

ℹ The 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.

Next question →

0 / 4

Share result Try again

Share to

Related terms

Related calculators

• ⚡
  Speed Converter

  Convert between mph, km/h, m/s, knots, and ft/s instantly. Free speed converter with quick-select conversions and a full real-world reference table.

• 📏
  Length Converter

  Convert between meters, kilometers, miles, yards, feet, inches, nautical miles, and more.