What is a mile?
A mile is an imperial and US unit of length, exactly 1,609.344 meters. The word comes from the Latin mille passus, 'a thousand paces', where a pace was two steps of a marching legionary.
A mile is equivalent to 1760yds or 5280ft.
Road distances in the US and UK are signed in miles, while nearly every other country uses kilometers. Aviation and shipping use the nautical mile instead, which is a different length (1,852 meters).
What is a UK Nautical Mile?
The UK nautical mile was based on one minute of latitude, ie 1/60th of a degree. The Earth is not a perfect sphere, so a minute of latitude varies slightly with latitude, which is why a fixed length had to be chosen.
The UK nautical mile, also called the Admiralty mile, was fixed at 6,080 feet, which is 1,853.184 meters. That is 1.184 meters longer than the international nautical mile of 1,852 meters (6,076.11549 feet), which the UK adopted in 1970.
How do you convert miles to UK nautical miles?
Multiply by 0.8684. A UK nautical mile is 6,080 ft against 5,280 ft for a statute mile, so the exact factor is 33/38, and 100 miles comes to 86.84 UK nautical miles.
Going the other way, a UK nautical mile is about 1.15 statute miles. The international nautical mile, exactly 1,852 m, is only 1.184 m shorter than the UK one, a difference you'd need a long voyage to notice.
Where are UK nautical miles used?
At sea the UK measures distance in nautical miles and speed in knots, as everywhere else. Since 1970 that has meant the international nautical mile of 1,852 meters, which replaced the older Admiralty mile of 6,080 feet.
The BBC Shipping Forecast gives visibility in nautical miles: 'good' means more than 5 nautical miles and 'poor' means between 1,000 meters and 2 nautical miles.
The UK's territorial sea reaches 12 nautical miles from the coast, so limits on shipping and fishing are given in the same unit.