Eli5: What’s the difference between a mile and a nautical mile


Eli5: What’s the difference between a mile and a nautical mile

In: 5678

I do not know where the statute mile came from but nautical miles are based on the size of the Earth. One nautical mile is one 60th of a degree of latitude.

Good answers above. As far as distance goes, a nautical miles is a little further than a mile. 10 knots is a little faster than 10mph (1.15 for every mile).

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 1.0×0.1 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.

A lot of units of measure are based on what was easy to measure for a person with ancient equipment.

On land, you don’t really need any equipment to measure a distance. Ancient people tended to measure things based on how many steps they took to get there. Sure, people are different sizes, but in general if 2 people walk “about 10,000 paces to the west” they’re close enough to a city or river that the differences in their strides are accounted for. So what ultimately became “a mile” on land was based on the distance a person could cover by taking a certain number of steps.

That doesn’t work so well at sea. The vast majority of humans can’t walk on water, and it’s exceptionally difficult to set up stationary landmarks to mark known distances. But people pretty quickly figured out they could use the position of the stars to get a pretty good idea of where they are, and while the equipment to do that is pretty fancy seafaring ships were also pretty expensive so it was worth installing fancy astrological equipment to help them navigate.

All of that math is based on spherical coordinates or “degrees”, so a nautical mile is based on a specific fraction of a degree. That was what was easy for sailors to measure, so it’s how they measured distance.

Lot of good info here about where nautical miles came from with respect to latitude/longitude, but the simple answer is:

A statute (normal) mile is 5280 feet.

A nautical mile is 1852 meters.


If you convert and subtract the two, a nautical mile is longer by about 800 feet.