When you're driving a car, speed is measured in kilometres per hour (km/h) or miles per hour (mph).

But on a ship, the captain might say:

"We're cruising at 20 knots."

Even airplanes use knots.

So why don't sailors simply use km/h?

The answer goes back hundreds of years to a simple rope with evenly spaced knots.

Before GPS and radar, sailors had no electronic instruments to measure speed.

Instead, they used a device called a chip log.

It consisted of:

As the ship moved forward, the wooden board stayed nearly stationary in the water while the rope unrolled behind the ship.

Sailors counted how many knots passed through their hands during a fixed amount of time.

The more knots counted, the faster the ship was traveling.

This is where the term "knots" originated.

Today, one knot is officially defined as:

1 nautical mile per hour

A nautical mile is 1.852 kilometres.

Unlike the standard mile or kilometre, the nautical mile is based on the Earth's geometry.

It equals one minute of latitude along the Earth's surface.

This makes it incredibly useful for navigation.

Ships and aircraft navigate using:

Since nautical miles are directly related to the Earth's coordinates, calculating distance and speed becomes much simpler.

For example:

If a ship travels at 20 knots for 3 hours, it has covered:

60 nautical miles

That distance matches perfectly with nautical charts.

Using kilometres would require constant conversions.

Interestingly, knots are not just for ships.

Aircraft also measure speed in knots because aviation navigation is based on nautical miles and geographic coordinates.

This ensures consistency between:

Whether crossing an ocean or flying across continents, everyone uses the same measurement.

Modern ships have advanced electronic navigation systems.

Yet the unit knot has survived because it remains the most practical measure for maritime and aviation navigation.

Sometimes, the oldest ideas continue because they're still the best.

The next time you hear a captain say a ship is traveling at 25 knots, remember something fascinating.

That word doesn't come from modern technology.

It comes from sailors counting knots tied into a rope hundreds of years ago.

A simple invention from the age of wooden sailing ships still guides the world's largest vessels and fastest aircraft today.

A knot is a unit of speed equal to one nautical mile per hour, or 1.852 km/h.

Because nautical miles align with the Earth's latitude and longitude, making navigation much easier.

Aircraft navigate using the same geographic coordinate system as ships, so knots provide a universal standard.

If you enjoy discovering the hidden stories behind transportation, technology, and everyday systems, subscribe to The Turning Pages Newsletter.

You will receive mind boggling origin stories about inventions, measurements, and traditions we encounter every day but rarely question.

Because once you start noticing these details, you will realize something fascinating.

The world is full of stories hiding in plain sight.