PHP

function getDistance($lat1, $lng1, $lat2, $lng2)

{

    $earth_radius = 6371;

    $dLat = deg2rad($lat2 - $lat1);

    $dLon = deg2rad($lng2 - $lng1);

    $a = sin($dLat/2) * sin($dLat/2) + cos(deg2rad($lat1)) * cos(deg2rad($lat2)) * sin($dLon/2) * sin($dLon/2);

    $c = 2 * asin(sqrt($a));

    $d = $earth_radius * $c;

    return $d;

}

MYSQL

CREATE FUNCTION distance_between (from_lat DECIMAL(6, 3), from_lng DECIMAL(6, 3), to_lat DECIMAL(6, 3), to_lng DECIMAL(6, 3)) RETURNS DECIMAL(11, 3)

    RETURN 6371 * 2 * ATAN2(SQRT(POW(SIN(RADIANS(to_lat - from_lat)/2), 2) + POW(SIN(RADIANS(to_lng - from_lng)/2), 2) * COS(RADIANS(from_lat)) * COS(RADIANS(to_lat))), SQRT(1 - POW(SIN(RADIANS(to_lat - from_lat)/2), 2) + POW(SIN(RADIANS(to_lng - from_lng)/2), 2) * COS(RADIANS(from_lat)) * COS(RADIANS(to_lat))));

JAVASCRIPT

function getDistanceFromLatLonInKm(lat1,lng1,lat2,lng2) {

    function deg2rad(deg) {

        return deg * (Math.PI/180)

    }

    var R = 6371; // Radius of the earth in km

    var dLat = deg2rad(lat2-lat1);  // deg2rad below

    var dLon = deg2rad(lng2-lng1);

    var a = Math.sin(dLat/2) * Math.sin(dLat/2) + Math.cos(deg2rad(lat1)) * Math.cos(deg2rad(lat2)) * Math.sin(dLon/2) * Math.sin(dLon/2);

    var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));

    var d = R * c; // Distance in km

    return d;

}