Geobytes City Distance Tool. Using equation (1) above, and substituting 4549 for s and using the earth’s diameter, divided in half, for the radius of earth re, the distance c is 4303 miles, a little Geobytes' free city distance tool allows you determine the distance between two international cities with the click of a button.

You can use it to to programmatically determine the service area of an ip address. The api returns the name, bearing, direction, latitude, longitude, and distance for each nearby city. The distance apart on the surface of the earth for them is 4549 miles.