What Is a Knot? Speed Unit Explained

4 min read•June 1, 2025•Reviewed: June 1, 2026

✓Reviewed by Apex Conversion Editorial Team · Last reviewed June 1, 2026

A knot is a unit of speed equal to one nautical mile per hour. It is the universal speed standard for aviation and maritime navigation worldwide — regardless of what country the pilot or captain is from. A ship traveling at 20 knots is moving at about 23 mph or 37 km/h.

The reason aviation and maritime navigation use knots instead of mph or km/h is geometric: nautical miles are directly tied to Earth's latitude lines, which makes navigation charts, position fixes, and distance calculations cleaner.

Conversion Values

1 knot = 1 nautical mile per hour
1 knot = 1.852 km/h   (exact)
1 knot = 1.15078 mph  (approximate)
1 knot = 0.514444 m/s

Reverse:
1 mph   = 0.868976 kn
1 km/h  = 0.539957 kn

Practical reference speeds:
  Typical cargo ship:  12–15 kn (22–28 km/h)
  Fast ferry:          30–40 kn (56–74 km/h)
  Commercial aircraft: 450–500 kn (833–926 km/h)
  Speed of sound:      about 661 kn at sea level

Why Knots for Navigation?

A nautical mile is defined as one arc-minute of latitude (1/60 of one degree) along Earth's surface — approximately 1,852 meters. This relationship to Earth's geometry means that on a navigation chart, the latitude scale is directly calibrated in nautical miles. One degree of latitude = 60 nautical miles, and distances can be measured directly off the chart using a compass and the latitude scale.

This geometric relationship made navigation drastically simpler in the age of paper charts and celestial navigation. Modern GPS has reduced this need, but knots remain universal in aviation and maritime navigation by convention, regulation, and the inertia of existing training and equipment.

Historical Origin of the Name

Before modern instruments, sailors measured ship speed with a 'chip log' — a piece of wood thrown overboard attached to a rope with evenly spaced knots tied at intervals. Sailors counted how many knots passed through their hands in a set time (typically 30 seconds) to estimate speed. The number of knots that passed gave the speed in 'knots' — which is why the unit persists today.

Frequently Asked Questions

How fast is 1 knot in mph?

1 knot equals approximately 1.151 mph or 1.852 km/h.

Why do planes use knots instead of mph?

Knots are used because aviation charts use nautical miles, and navigation calculations (time to destination, fuel burn rate) are simpler when speed and distance use the same base unit. It is also the internationally standardized unit for air traffic control worldwide, eliminating any confusion between countries with different speed unit conventions.

What is Mach 1 in knots?

Mach 1 (the speed of sound) is approximately 661 knots at sea level in standard conditions (343 m/s). The Mach number itself isn't fixed — it varies with altitude and temperature, which is why pilots typically refer to both airspeed in knots and Mach number.

Try the Speed Converter

🚀 Open Speed Converter →