php function to calculate the distance between co-ordinates

Just a little PHP function to calculate the distance between two coordinates. You can specify the units to be returned also.

function distance($lat1, $lon1, $lat2, $lon2, $unit) { 
  $theta = $lon1 - $lon2; 
  $dist = sin(deg2rad($lat1)) * sin(deg2rad($lat2)) +  cos(deg2rad($lat1)) * 
    cos(deg2rad($lat2)) * cos(deg2rad($theta)); 
  $dist = acos($dist); 
  $dist = rad2deg($dist); 
  $miles = $dist * 60 * 1.1515;

  $unit = strtoupper($unit);

  if ($unit == "K") {

    return ($miles * 1.609344); 

  } else if ($unit == "N") {
      return ($miles * 0.8684);
  } else {
        return $miles;
  }
}

Usage is:

echo distance(32.9697, -96.80322, 29.46786, -98.53506, "m") . " miles";

Hope that’s of some use to someone. You can co-ordinate it with a function to get the lat-long of a pair of zip codes, and then calculate shipping distance for example.