Eli5: Whats the Difference Between a Mile and a Nautical Mile

Kent - March 6, 2023


Nautical mile is 1 minute (1/60) of a degree of lattitude. Cut the planet in half and divide the circle into 21,600 segments. Each segment of the circumference (surface at sealevel) is a nautical mile.

Why? When you’re in the middle of the ocean, you can only really look up at the stars and measure angles to figure out when you are.

A “normal” mile.

This is the short version of the story. (With many things condensed or altered for easier understanding)

The romans were neat and tidy. A pace was 2 steps and 5 feet long (different feet than we use). A roman mile was 1000 paces or 5000 feet. 1/8th of a mile (625 feet) is called a stadia (this is where the term stadium comes from.. guess how long the Colosseum is).

The romans marched to England.

The english had their own measures, importantly, the furlong.

When you plough a field, you make furrows in the ground. The length you go before resting your animal is a furrows length, a “furlong.” The area you plough in a day is an acre. (Officially, it is a 1.0x0.1 area)

An acre is, by definition, 1 furlong in length… this is important.

The furlong and the stadia were similar in length. Why use the foreign word when you already have a word for it?. They became synonymous.

A furlong is Officially 220 yards or 660 feet. (The acre is 22 yards/66 feet wide. This length is called a chain because surveyors used 100 link chains of 22 yards to measure land).. remember, the stadia is 625 feet.

This didn’t matter right up until it did. Tax!

Land area measures are important for a lot of things but tax was a big one. Having a mess in the middle distances and area measures was a problem.

England had a choice. Shorten the furlong and acre and reduce all the smaller units too (affecting everyones daily life), or, make the mile longer.

Distance Officially starts with a grain of barley. 3 laid end to end makes 1 inch. 12 inches makes a foot (inch literally means 1/12th), 3 feet make a yard, 5.5 yards make a perch/rod (not common anymore), 40 perches make a furlong (chains are more modern), an acrea is 40 perches long and 4 perches wide, and furlong keeps getting the be 1/8th of a mile so the mile is now 1760 yards or 5280 feet.

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