What's the Difference Between a Nautical Mile and a Mile?

By: HSW Contributors  | 
large sailboats racing
The nautical mile is a marine navigation distance measurement that has its roots in the very shape of our planet. Pavel Nesvadba/Shutterstock

When it comes to measuring distance, whether on land, in the air or at sea, having an accurate unit is vital. We're all familiar with the common land-measured mile, but many may not realize that there's another unit of measurement used in maritime and aviation settings: the nautical mile. Understanding the difference between a nautical mile and a land mile is crucial in navigational calculations.


Nautical Mile vs. Mile

A nautical mile is slightly longer than the standard, or "statute," mile we use in our daily lives, coming in at approximately 1.1508 land miles. However, this isn't just an arbitrary difference. The nautical mile has its roots in the very shape of our planet. Based on Earth's longitude and latitude coordinates, 1 nautical mile corresponds to one minute of latitude. One minute of latitude is about 1.1 miles (1.8 kilometers) and one second of latitude covers about 105 feet (32 meters).

In the English measurement system, there is 1 nautical mile per 1.1508 land miles or 6,076 feet. One nautical mile is a length equal to 1,852 meters, or 1.852 kilometers.


Why the Two Measurements?

The primary reason for using a different measurement system for marine and aviation navigation relates to the curvature of the Earth. As you embark on long-distance travel, Earth's round shape becomes a factor in accurate measurement. Nautical charts employ latitude and longitude, making it much simpler for mariners, pilots and astronauts to measure distances using nautical miles, offering a more precise representation of the route traveled.

A nautical mile is based on the circumference of planet Earth. If you were to cut Earth in half at the equator, you could pick up one of the halves and look at the equator as a circle. You could divide that circle into 360 degrees. You could then divide a degree into 60 minutes. A minute of arc on the planet Earth is 1 nautical mile. Nautical miles as units of measurement are used by all nations for air and sea travel.


Understanding International Nautical Miles

Now, you might wonder whether there is an equivalent "nautical kilometer" in the metric system. Interestingly, there isn't a kilometer equivalent for nautical miles. Instead, the international nautical mile, set at exactly 1.852 kilometers, is used worldwide.

A kilometer is also defined using planet Earth as a standard of distance. If you were to take Earth and cut it in half along a line passing from the North Pole through Paris, measure the distance of the curve running from the North Pole to the equator on that circle, and then divide that distance by 10,000, you would have the traditional unit for the kilometer as defined in 1791 by the French Academy of Sciences.


The International Hydrographic Organization standardized this measurement in 1929. Following this official setting, the United States and the United Kingdom used slightly different measurements for a period of time. However, the U.S. adopted the international nautical mile in 1954, followed by the U.K. in 1970. The international nautical mile set by the International Hydrographic Organization has been the standard for sea and air travel since then, unifying measurements globally and simplifying navigation across different regions.

Speed on the High Seas: Knots and Their Origins

A knot is a unit of measurement for speed. If you are traveling at a speed of 1 nautical mile per hour, you are said to be traveling at a speed of 1 knot.

While nautical miles measure distance, knots are the unit of choice when it comes to speed in maritime and aviation contexts. One knot equals 1 nautical mile per hour, or about 1.15 statute miles per hour, neatly tying speed to distance in this unique environment.


The term "knot" harks back to the 17th century, where it found its origin in an innovative seafaring tool known as the "common log." Sailors measured using this device, a rope knotted with uniformly spaced knots attached to a pie slice-shaped piece of wood, to estimate their ship's speed. The sailors would lower the wood into the water, letting it float freely behind the vessel for a specific amount of time. Once the time elapsed, typically measured with an hourglass, they would count the knots between the ship and the wooden piece to estimate their speed.

To travel around Earth at the equator, you would have to travel 21,600 nautical miles, 24,857 statute miles or 40,003 kilometers.

Understanding the nuanced differences between a nautical mile, a statute mile and a knot is more than just an interesting tidbit of trivia; it's a critical component of global navigation, enabling precise and consistent measurements across sea, air and space. The next time you're out sailing, flying or simply looking at a nautical chart, you'll appreciate the thoughtful calculations behind these unique measurements.

This article was updated in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.