Definition
A unit of distance used in aviation and marine navigation, equal to 1,852 meters or approximately 6,076 feet. One nautical mile corresponds to one minute of arc of latitude along any meridian of the Earth, which is what makes it useful for navigation on charts.
Plain English
A nautical mile is the standard unit pilots use to measure distance. It is a bit longer than the everyday land mile (a statute mile) — about 1.15 land miles for every nautical mile.
Context Anchor
Seen in performance charts, flight planning, navigation displays, and distance statements such as range or distance to an airport.
Derivation
The word nautical comes from the Latin nauticus, meaning 'relating to ships or sailing.' The nautical mile originated in marine navigation because it ties directly to the geometry of the Earth — one minute of latitude equals one nautical mile. That same convenience is why aviation adopted it.
Why Pilots Care
All performance numbers such as range, fuel planning, and glide distance are expressed in nautical miles, so using the wrong unit produces incorrect results.
Intuition Check
Do not read NM as a regular road mile. One NM is about 15 percent longer than one road mile.
Example Sentence 1
The airport was 45 NM to the northeast, so at a groundspeed of 90 knots the flight would take about 30 minutes.
Example Sentence 2
With an 8-to-1 glide ratio the airplane can reach any field within 16 NM from 2,000 feet AGL.