Calculate distance between two points in google maps V3

Example using GPS latitude/longitude of 2 points.

var latitude1 = 39.46;
var longitude1 = -0.36;
var latitude2 = 40.40;
var longitude2 = -3.68;

var distance = google.maps.geometry.spherical.computeDistanceBetween(new google.maps.LatLng(latitude1, longitude1), new google.maps.LatLng(latitude2, longitude2));       

There actually seems to be a method in GMap3. It's a static method of the google.maps.geometry.spherical namespace.

It takes as arguments two LatLng objects and will utilize a default Earth radius of 6378137 meters, although the default radius can be overridden with a custom value if necessary.

Make sure you include:

<script type="text/javascript" src="http://maps.google.com/maps/api/js?sensor=false&v=3&libraries=geometry"></script>

in your head section.

The call will be:

google.maps.geometry.spherical.computeDistanceBetween (latLngA, latLngB);

If you want to calculate it yourself, then you can use the Haversine formula:

var rad = function(x) {
  return x * Math.PI / 180;
};

var getDistance = function(p1, p2) {
  var R = 6378137; // Earth’s mean radius in meter
  var dLat = rad(p2.lat() - p1.lat());
  var dLong = rad(p2.lng() - p1.lng());
  var a = Math.sin(dLat / 2) * Math.sin(dLat / 2) +
    Math.cos(rad(p1.lat())) * Math.cos(rad(p2.lat())) *
    Math.sin(dLong / 2) * Math.sin(dLong / 2);
  var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
  var d = R * c;
  return d; // returns the distance in meter
};