This script calculates great-circle distances between the two points – that is, the shortest distance over the earth’s surface – using the ‘Haversine’ formula.

It assumes a spherical earth, ignoring ellipsoidal effects – which is accurate enough* for most purposes… – giving an ‘as-the-crow-flies’ distance between the two points (ignoring any hills!).

Enter the co-ordinates into the text boxes to try it out. It accepts a variety of formats:

Lat 1: Long 1:

Lat 2: Long 2:

And you can see it on a map (thanks to the nice guys at Google Maps)