If you’ve ever looked at a ship’s or plane’s speed and noticed it’s given in knots, you might have wondered why this unit is still used. Unlike kilometers per hour or miles per hour, knots have a unique history and practical advantages that make them ideal for navigation.

The origin of the knot dates back to early sailors. To measure speed, they used a log line—a rope with knots tied at regular intervals—thrown overboard while the ship was moving. By counting how many knots passed through their hands in a set period of time, sailors could estimate the ship’s speed. This simple but effective method gave the unit its name.

One knot equals one nautical mile per hour. Nautical miles differ from standard miles or kilometers because they are based on the Earth’s geometry, aligning with latitude and longitude. This makes knots extremely useful for plotting courses over long distances, both at sea and in the air. Using knots ensures that distance, speed, and navigation remain consistent across charts, routes, and flight plans.

Modern ships and aircraft continue to use knots because they provide a universal standard. Whether it’s a cargo ship crossing oceans or a commercial airliner flying between countries, knots allow crews to communicate speed accurately and coordinate with navigation systems. Wind speeds are also reported in knots, helping pilots and mariners account for environmental conditions and maintain safety.

Typical cruising speeds vary depending on the vessel or aircraft. Passenger ships travel around 20–25 knots, fast ferries can reach 30–40 knots, and commercial airplanes cruise at roughly 450–500 knots. Even military jets, which fly much faster, often reference knots for navigation and planning.

Knots are more than a historical tradition—they are a practical, reliable unit that connects past navigation methods to today’s high-tech world. By understanding why mariners and pilots measure speed in knots, we can better appreciate how people move safely and efficiently across the seas and skies.