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Statute Miles vs. Nautical Miles

Thanks to Michelle d'Aoust for a very precise and detailed answer on how to convert to/from nautical miles:

A statute mile is 5,280 feet in length.
A nautical mile is 6,076.11549... feet in length.

To convert from statute to nautical miles a factor of 1.15 is generally used, even though it is not precise.

(5,280 feet X 1.15) = 6,072 feet (4.11549...feet less than 1 nautical mile).You could add 4.1 feet for each statute mile to be converted. So the new formula would be: {(5280 feet x 1.15)+ 4.1 feet} divided by 6,076.1 feet = 1 nautical mile.

To convert from nautical to statute miles: The factor 1.15 may be used, but again, it is not precise.

(6076.1 divided by 1.15) = 5,283 feet (3.565..feet more than 1 statute mile). Using a precomputed table (such as Bowditch's Table 20) will result in the more precise answers.


Comments:

For a less precise answer "Chapmans Piloting and Small Boat Handling" suggests:

statute miles x .87 = nautical miles

nautical miles x 1.15 = statute miles

As a rule of thumb, roughly 7 nautical miles equals 8 statute miles. You can convert nautical to statute by multiplying nautical miles by 8 and dividing the product by seven. To reverse the conversion, statute miles times 7, then divide by 8.

A Nautical Mile is 1/60th of a degree or one minute of latitude. Be sure you know what distance measurement is being used on the charts you are working with. There are four common measures of distance used on charts:

And from Alan Richard - "As a point of interest, Florida boating and marine fisheries laws still express distance in leagues, as in Jules Verne's 20,000 Leagues Under the Sea. A marine league is three nautical miles."

Capt. Matt

Related Articles:
All About Nautical Charts
Nautical Chart Reading 101
How to use Dividers and Parallel Rulers
Identifying Aids to Navigation
Regulatory Markers
Boating Safety Course

Also see The Coastal Navigation Course

 

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