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What Is a Knot and How Fast Is It?

A knot is a unit of speed used almost exclusively in maritime and aviation contexts.

One knot is equal to one nautical mile per hour.

• 1 knot = 1.15 miles per hour (mph)
• 1 knot = 1.852 kilometers per hour (km/h)

The abbreviation for a knot is "kt" or "kts" for the plural.

Why Is a Ship's Speed Called a "Knot"?

The term "knot" dates back to the 17th century, when sailors measured their ship's speed using a tool called a "chip log."

This device worked in a simple but clever way:

• A rope was tied with knots at regular intervals (every 47 feet and 3 inches).
• One end of the rope was attached to a piece of wood (the "chip") and thrown into the water behind the ship.
• As the ship moved forward, the rope would unspool. Sailors would count how many knots passed through their hands in 28 seconds, measured with a sandglass.

The number of knots they counted directly corresponded to the ship's speed in "knots."

How Is a Knot Connected to the Earth's Size?

A knot isn't a random measurement—it's directly linked to the Earth's circumference. To understand this, you need to know about the nautical mile.

A nautical mile is based on the Earth's coordinates of longitude and latitude. It is equal to exactly one minute (1/60th of a degree) of latitude.

Since a knot is one nautical mile per hour, it integrates seamlessly with all nautical and aeronautical charts.

This makes navigation and distance calculations much simpler for pilots and captains.

• 1 Nautical Mile = 1.852 kilometers (or 1,852 meters)
• 1 Nautical Mile = 6,076 feet

Why Do Planes and Ships Still Use Knots Today?

On land, we use miles per hour or kilometers per hour, but in the air and at sea, speed is measured in knots — and for good reason.

A knot is one nautical mile per hour, and a nautical mile is tied to the Earth's lines of latitude.

That direct link to the globe enables knots to work seamlessly with navigation charts, simplifying distance, travel time, and course calculations.

Using knots as a universal standard ensures that pilots, sailors, and air traffic controllers all speak the same language—an essential factor for global safety and coordination.