All aviators and mariners are familiar with a nautical mile, which is the distance subtended by one degree of latitude at sea level. If you know the latitude and longitude of two different places, it is a simple calculation to determine the distance between them, measured in nautical miles, and a further simple calculation to convert that figure into statute miles.
Write down the latitudes and longitudes in degrees of the two places. If both places are in the same hemisphere, calculate the difference between the latitudes and longitudes. If they are in different hemispheres, they must be added together.
Example 1. Place A 25 degrees North Place B 52 degrees North, difference = 27 degrees
Example 2. Place A 25 degrees North Place B 52 degrees South, difference = 77 degrees
Example 1. Place A 50 degrees West Place B 120 degrees West, difference = 70 degrees
Example 2. Place A 50 degrees West Place B 120 degrees East, difference = 170 degrees
Use a calculator to calculate the square of the difference in latitude and the square of the difference in longitude and add them together. Calculate the square root of this product and multiply by 60. This will give you the distance in nautical miles between the two places. To convert this distance into statute miles, multiply the result by 1.15
Using the figures in example 1 we have 27 squared plus 70 squared giving a result of 729 + 4,900, or 5,629. The square root of this figure is 75. When multiplied by 60 the result is 4,500 nautical miles or 5,175 statute miles.
There are several websites (see below) that will do the calculation for you--all you have to do is to enter the figures.
This method gives an approximate distance only. It is more accurate closer to the Equator. The closer a place is to the North or South Poles, the less accurate is the result.