Why is a Ship’s Speed Measured in Knots?

When we drive a car or ride a bike, our speed is measured in miles per hour or kilometers per hour. But when you get in a boat, those measurements change, and the term knot is used to measure how fast you’re going. Why are knots used for the speed on water? It actually comes from something that was done long ago.

Crews of sailing ships far back in history didn’t have the advantage of GPS or modern maps. They had to use what they had around them to determine where they were going and how long it would take get there. Knowing the speed of a ship’s travel was vital. Without it, the crews of these ships could find themselves so far off course that it would prove deadly. Knowing exactly how fast a ship was going was imperative for navigation and when a ship would arrive at its destination.

The knot sounds like it has to do with rope, and that would be correct. The term knot originated in the 17th century and is based on the length of the nautical mile. A nautical mile is based on the circumference of the earth, and it is equal to one minute of latitude. The mile we are familiar with on land is the statute mile, and a nautical mile is slightly longer (1 nautical mile = 1.1508 statute miles).