Knot (kn) - Unit Information & Conversion

Definition

The knot (kn) is a unit of speed equal to one nautical mile per hour, which is exactly 1.852 km/h (approximately 1.15078 mph or 0.514 m/s).

History

The term knot originates from the 17th century practice of measuring ship speed using a "chip log". This device consisted of a rope with knots tied at uniform intervals (47 feet 3 inches or 14.4018 m), attached to a piece of wood shaped like a sector of a circle. The log was thrown overboard, and sailors counted the number of knots that passed through their hands in a specific time (usually measured by a 28-second sandglass). The number of knots counted in that time directly corresponded to the ship's speed in nautical miles per hour.

Common Uses

• Maritime Navigation: The primary unit for measuring vessel speed in maritime contexts worldwide.
• Aviation: Standard unit for indicating airspeed for aircraft globally.
• Meteorology: Commonly used to report wind speeds, especially in forecasts for marine and aviation purposes.

Unit FAQs

What is a knot based on?

A knot is equal to one nautical mile per hour. A nautical mile is based on the Earth's circumference (one minute of latitude).

Is the knot an SI unit?

No, the knot is not an SI unit, but it is accepted for use with the SI, especially in navigation.

Why are knots used instead of mph or km/h in navigation?

Knots are convenient because one knot is one nautical mile per hour, and a nautical mile directly relates to the lines of latitude and longitude on navigational charts (one nautical mile is approximately one minute of latitude).

How do you convert knots to mph?

Multiply the speed in knots by approximately 1.151. So, 20 knots is about 23 mph.

How do you convert knots to km/h?

Multiply the speed in knots by 1.852. So, 20 knots is exactly 37.04 km/h.