Vincenty formula for distance between two Latitude/Longitude points

Thaddeus Vincenty (‘TV’) devised formulae for calculating geodesic distances between a pair of latitude/longitude points on the earth’s surface, using an accurate ellipsoidal model of the earth.  Vincenty’s formula is accurate to within 0.5mm, or 0.000015″ (!), on the ellipsoid being used. Calculations based on a spherical model, such as the (much simpler) Haversine, are accurate to around 0.3% (which is still good enough for most purposes, of course).  See the ‘Direct’ formula to calculate the destination point given the start point, bearing and distance.

Enter the co-ordinates using deg-min-sec suffixed with N/S/E/W, or signed decimal degrees:

Lat 1: Long 1:

Lat 2: Long 2:

Note: the accuracy quoted by Vincenty applies to the theoretical ellipsoid being used, which will differ (to varying degree) from the real earth geoid. If you happen to be located in Colorado, 2km above msl, distances will be 0.03% greater. In the UK, if you measure the distance from Land’s End to John O’ Groats using WGS-84, it will be 28m – 0.003% – greater than using the Airy ellipsoid, which provides a better fit for the UK.