Nautical Miles and Knots: Why Pilots and Sailors Use Them

Aircraft and ships measure distance in nautical miles and speed in knots. These units aren't old-fashioned leftovers: they're tied to the shape of the Earth, which makes navigating with charts easier.

The nautical mile

One nautical mile (NM) is defined as exactly 1,852 meters. It was originally based on one minute of latitude, 1/60 of a degree, so 60 nautical miles is about one degree of latitude anywhere on Earth. That lets navigators measure distances directly against the latitude scale on the side of a chart.

The knot

A knot is one nautical mile per hour.

• 1 knot = 1.852 km/h exactly
• 1 knot ≈ 1.151 mph
• 1 knot ≈ 0.514 m/s

A jet cruising at 480 knots is doing about 889 km/h, or 552 mph.

Converting distances

• Nautical miles to kilometers: multiply by 1.852
• Nautical miles to statute miles: multiply by 1.151
• Kilometers to nautical miles: divide by 1.852

Estimating travel time

A 300 NM sailing passage at an average of 6 knots takes 50 hours. A 900 NM flight at a ground speed of 450 knots takes 2 hours.

Airspeed vs. ground speed

For aircraft, wind matters. Ground speed is airspeed adjusted for wind: a plane flying at 450 knots into a 50-knot headwind covers the ground at roughly 400 knots, which adds time to the trip. A tailwind does the opposite. Currents have the same effect on boats.

Headings in degrees

Courses are given in degrees clockwise from north: 090° is east, 180° is south and 270° is west. Navigators also correct for magnetic variation, the difference between true north and magnetic north, which changes with location.

This guide is for general interest only, not for navigation or flight planning.