Definition
A unit of speed equal to one nautical mile traveled in one hour, equivalent to one knot. One nautical mile is 6,076 feet, slightly longer than a statute mile (5,280 feet), so one nautical mile per hour is about 1.15 statute miles per hour.
Plain English
How fast something is moving when it covers one nautical mile every hour. Saying 'nautical miles per hour' is the same as saying 'knots.'
Context Anchor
Seen in airspeed, groundspeed, wind, drift, and ground track discussions, especially when matching aircraft speed to chart distances.
Derivation
Nautical' comes from the Latin nauticus, meaning 'relating to ships or sailing.' Aviation inherited the nautical mile from marine navigation because it ties neatly to latitude on a chart — one nautical mile equals one minute of arc along a meridian. That makes distance and position easy to read straight off a chart, which is why pilots use it instead of the statute mile.
Why Pilots Care
All airspeed, groundspeed, and wind-correction calculations in aviation are performed in this unit; using statute miles per hour instead produces navigation and performance errors.
Intuition Check
Do not read this as regular miles per hour from a car speedometer. In aviation, nautical miles per hour uses nautical miles, so it is not the same distance per hour as ordinary road miles per hour.
Example Sentence 1
The airplane was making good 110 nautical miles per hour across the ground, which the pilot read directly as 110 knots on the GPS.
Example Sentence 2
With a 15-knot headwind the groundspeed dropped to 95 nautical miles per hour.