top of page

Why are flight distances in miles?

Updated: Sep 20, 2023

A great and interesting question, I should have put this in a blog sooner! Thank you to the person who asked me, why my flightlog booklet was in "miles". Keep the questions coming, I am always looking for new content and ideas.

I haven't gotten too technical here but living in Greenwich, UK where time literally begins, with history of time and space all around me, I am always fascinated by this topic. See the Fun Facts section for more about the Prime Meridian, when countries adopted the international nautical mile measurement, etc.

Flights use a measurement called Nautical Miles

BA plane suspended between cranes. coming into land
Plane coming into land (suspended, for a moment, between cranes). Photo credit: ©CRiney2019

Nautical Miles

world map with longitude and latitude lines
Longitude and Latitude lines - 0 =Greenwich Meridian

Before air and space travel, nautical miles, were, and still are used to measure the distance traveled through the water. A nautical mile is slightly longer than a mile on land, equaling 1.1508 land-measured (or statute) miles. The nautical mile is based on the Earth’s longitude and latitude coordinates, with one nautical mile equaling one minute of latitude.

Nautical miles are used because they are equal to a specific distance measured around the Earth. Since the Earth is circular, the nautical mile allows for the curvature of the Earth and the distance that can be traveled in one minute.

Why use a different measurement for Sea Navigation?

This is because using latitude and longitude coordinates is more practical for long-distance travel, where the curvature of the Earth becomes a factor in accurate measurement. Nautical charts use latitude and longitude, so it’s far easier for mariners to measure distance with nautical miles.

Air and Space Travel

This is earth curvature is the reason that air and space travel also use latitude and longitude for navigation and nautical miles to measure distance.

Why not use the metric system?

The word “mile” might leave you wondering if there’s a “nautical kilometer,” too. There’s not. The international nautical mile is used throughout the world. The measurement was officially set at exactly 1.852 kilometers in 1929 by what is now known as the International Hydrographic Organization.

Fun Facts:

1. International Nautical Mile - The U.S. and the United Kingdom both use to use slightly different measurements after that time, but the U.S. adopted the international nautical mile in 1954 and the U.K. in 1970.

2. Prime Meridian - "The prime meridian is zero degrees longitude and divides Earth into the Western and Eastern hemispheres. It is also known as the Greenwich Meridian because it passes through Greenwich, a borough of London, and terminates at the North and South poles. The meridian is also a key element in timekeeping, as in the 12-hour clock."

Greenwich Meridian at the Greenwich Observatory - photo credit: ©CRiney2023 & AMestrov2023

3. Knots - "Ancient mariners used to gauge how fast their ship was moving by throwing a piece of wood or other float-able object over the vessel’s bow then counting the amount of time that elapsed before its stern passed the object. This method was known as a Dutchman’s log." Boats & Planes calculate speed in knots which is equal to one nautical mile.

4. Nautical miles & knots - A nautical mile measures distance and a knot measures speed. Nautical miles are used for charting and navigating. A knot is one nautical mile per hour (1 knot = 1.15 miles per hour ).

Thanks for reading, hope you found it interesting! For my flightlog, click here. For general information about my travelogs, click here.

57 views2 comments

Recent Posts

See All


Apr 21, 2023

If you want to check the nautical mile distances for a journey, try using Great Circle Mapper at In the box, enter your journey using airport three letter codes. For example, enter Heathrow-Singapore-Sydney as LHR-SIN-SYD. Click on the "Map" button. This draws your great circle route (the shortest route). Below the map you'll see the distances. They'll usually come up in statute miles. To display nautical miles, scroll down to Map Controls. Click the tab "Dist+Time" and change the units to nautical miles. Click on Map again and you'll find out the distances in the traditional navigational units.

You'll also see why the closure of Ukrainian and Russian airspace is forcing airlines to take sub-optimal routes to Asia!

Apr 21, 2023
Replying to

Thank you for your comment, Edmond! Yes, the Great Circle Mapper is a great tool. You can find more info and examples on my site at . I also use the tool to calculate journeys I have done! Love that it has the up to date airspace info - I will check that out.

Happy Travels, Catherine at Our World Travel Logs😊

bottom of page