Get Distance From Latitude and Longitude in Kilometers

geo_distance.js

function getDistanceFromLatLonInKm(lat1, lon1, lat2, lon2) {
    var R = 6371, // Radius of the earth in km
        dLat = deg2rad(lat2 - lat1),  // deg2rad below
        dLon = deg2rad(lon2 - lon1),
        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),
        c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a)),
        d = R * c; // Distance in km

    return d;
}

function deg2rad(deg) {
    return deg * (Math.PI / 180);
}