What Is A Nautical Mile? What Is A Knot?
If you've spent any time around boats, you've heard distances measured in nautical miles and speed measured in knots rather than the kilometres and kilometres per hour used on land. Here's what these units actually mean, and where the term "knot" comes from.
What Is A Nautical Mile?
A nautical mile is a unit used to measure distances at sea, in the air, and in space travel. It's equal to 1,852 metres, or 1.852 kilometres. In the English measurement system, that converts to 1.1508 miles, or 6,076 feet. Unlike a standard mile, a nautical mile is based on the circumference of the Earth. It's defined as equal to one minute of latitude, which is why it's used consistently in maritime and aviation navigation around the world.
What Is A Knot?
A knot is a unit of speed. If you're travelling at one nautical mile per hour, you're travelling at a speed of one knot.
Why Is A Knot Called A Knot?
The term dates back to the 17th century, when sailors measured a ship's speed using a device called a common log, also known as a chip log or ship log. This was a coil of rope with uniformly spaced knots, attached to a piece of wood.
The wood was lowered from the back of the ship and allowed to float behind it while the line played out freely for a set amount of time, usually measured with a small sand-glass. Once the time had elapsed, the crew pulled the line back in and counted the number of knots that had passed between the ship and the floating wood. That count gave the ship's speed in what became known as knots (Bowditch, 1984).
Understanding nautical miles and knots is one of those small pieces of boating knowledge that makes navigation, weather reports and boat specifications far easier to follow.
Want to brush up on more boating terminology? Check out our full glossary of commonly used boating terms on Boats Online.
Frequently Asked Questions
How many kilometres is a nautical mile?
A nautical mile is equal to 1.852 kilometres, or 1,852 metres.
How many knots is one nautical mile per hour?
Travelling at one nautical mile per hour is, by definition, travelling at a speed of one knot. The two are directly equivalent.
Why do sailors use nautical miles instead of regular miles?
A nautical mile is based on the Earth's circumference, defined as one minute of latitude, which makes it directly useful for navigation calculations at sea and in the air. This is why it's the standard unit for maritime and aviation distance worldwide.
Where does the term "knot" come from?
The term comes from a 17th-century device called a common log, a rope with evenly spaced knots attached to a piece of wood. Sailors counted how many knots passed by in a set amount of time to calculate the ship's speed, and the unit name stuck.
