A nautical mile (NM) is most commonly associated with traveling through water, as is using knots to determine boat speed. However, both are used in airplanes, too. NMs are used to navigate the open skies and vast oceans because they account for the Earth’s curvature. Once air travel became a reality, the industry quickly discovered that the system sailors used worked just as well for pilots. When Charles Lindbergh successfully used it to navigate his transatlantic flight in 1927, he cemented its future use. Today, they help give pilots a more accurate idea of how much fuel they will consume.
When ancient mariners began spreading out across the globe, they discovered the Earth’s round shape posed a problem for accurately measuring distances. The creation of longitude, latitude, and coordinates fixed that problem. Throughout much of that seafaring history, one nautical mile was only defined as one minute arc of latitude along any line of longitude. In 1929, the First International Extraordinary Hydrographic Conference was held in Monaco, and the NM was set to exactly 1,852 meters, which equated to the rather clumsy distance of 1.151 miles or 6,076 feet. In constrast, a “statute mile” is 5,280 feet.
Longitude and Latitude and nautical miles, oh my!
The nautical mile not only makes flight safer but also supports modern GPS-based navigation. Both the International Civil Aviation Organization (ICAO) and the International Maritime Organization (IMO) require the use of nautical miles as a global standard for ships and aircraft. Interestingly, the U.K. didn’t adopt the international nautical mile until 1970, while the U.S. did so in 1954. If you’re wondering, there’s no such thing as a “nautical kilometer,” as the globally agreed-upon international distance was set using kilometers, not miles, even though the term “mile” is used in the name.
Back in 1947, the ICAO passed a resolution to standardize the unit of measure and even created something called the International System of Units. Based on the metric system, the idea was to phase out the use of “nautical mile” and “knot” (equal to 1 NM/h) in a slow, deliberate manner so as not to rock the boat. Oddly, the system was adopted in 1960 by the 11th General Conference on Weights and Measures (CGPM), but not by the global aviation or naval industries. As of this writing, the nautical mile still wasn’t part of the system. Although “M,” “NM,” “Nm”, and “nmi” have all been used interchangeably over the years, no agreed-upon standard has been established.

