Calculating Distance between two Latitude and Longitude Geo Coordinates

//Calculate distance by cordinates
        public static double CalculateDistance(string unit, double latitude1, double lon1, double latitude2, double lon2)
        {
            var theta = lon1 - lon2;
            var dist = Math.Sin(DegreetoRadian(latitude1)) * Math.Sin(DegreetoRadian(latitude2)) + Math.Cos(DegreetoRadian(latitude1)) * Math.Cos(DegreetoRadian(latitude2)) * Math.Cos(DegreetoRadian(theta));
            dist = Math.Acos(dist);
            dist = RadiantoDegree(dist);
            dist = dist * 60 * 1.1515;// Miles as default
            switch (unit)
            {
                case "Kilometers":
                    dist = dist * 1.609344;
                    break;
                case "NauticalMiles":
                    dist = dist * 0.8684;
                    break;
            }
            return (dist);
        }

        //Converts decimal degrees to radians
        public static double DegreetoRadian(double deg)
        {
            return (deg * Math.PI / 180.0);
        }

        //Converts radians to decimal degrees
        public static double RadiantoDegree(double rad)
        {
            return (rad / Math.PI * 180.0);
        }