Distance between two points / coordinates

Latitude and Longitude in the formula must be radians, example: Lat1 = Lat1 * PI / 180
6378.137 is diameter of earth in kilometers (WGS84 datum). Use: 3963.191 for miles.

			PI = 3.14159265358979323846
Lat1 = Lat1 * PI / 180
Lon1 = Lon1 * PI / 180
Lat2 = Lat2 * PI / 180
Lon2 = Lon2 * PI / 180
D = 6378.137 * ACos( Cos( Lat1 ) * Cos( 
			Lat2 ) * Cos( Lon2 - Lon1 ) + Sin( Lat1 ) * Sin( Lat2 ) )
		

If your programming language or application does not have ACos function, maybe has Atn, use the following formula instead to calculate via ArcTan mathematical function.
Provide Latitude and Longitude as decimals, no need to convert them to radians.

			D = 6378.137 * Atn( Sqr( ( 1 - ( Sin( Lat1 / 57.29577951 ) * Sin( 
			Lat2 / 57.29577951 ) + Cos( Lat1 / 57.29577951 ) * Cos( 
			Lat2 / 57.29577951 ) * Cos( Lon2 / 57.29577951 - 
			Lon1 / 57.29577951 ) ) ^2 ) ) / (Sin ( Lat1 / 57.29577951 ) * Sin( 
			Lat2 / 57.29577951 ) + Cos( Lat1 / 57.29577951 ) * Cos( 
			Lat2 / 57.29577951 ) * Cos( Lon2 / 57.29577951 - 
			Lon1 / 57.29577951 ) ) )
		

Code samples:

Java

ASP

C+

Perl

PHP

Const PI = 3.14159265358979323846
Const Radius = 6378.137

Dim Lat1 = 41.3879169;
Dim Lon1 = 2.1699187;
Dim Lat2 = 40.4167413;
Dim Lon2 = -3.7032498;

'Units: K=kilometers  M=miles  N=nautical miles
Dim Unit = "K"

Dim Result

Result = Distance( Lat1, Lon1, Lat2, Lon2, Unit ) & " kilometers"

msgbox(Result)

Function Distance( Lat1, Lon1, Lat2, Lon2, Unit )
  Dim dlon, distance
  Lat1 = cdbl(Lat1 * PI / 180)
  Lon1 = cdbl(Lon1 * PI / 180)
  Lat2 = cdbl(Lat2 * PI / 180)
  Lon2 = cdbl(Lon2 * PI / 180)
  DLon = Lon1 - Lon2
  
  Distance = ACos (sin(Lat1) * sin(Lat2) + cos(Lat1) * cos(Lat2) * cos(DLon) ) * Radius

Select Case lcase(unit)
    Case "K"
      Distance = Distance
    Case "M"
      Distance = Distance * 0.621371192
    Case "N"
      Distance = Distance * 0.539956803
  End Select
End Function

' ----------------------------------------------------------------------------------
'  Calculates ArcCos: acos() funtion (not available) by using Arctan: atn() function   
' ----------------------------------------------------------------------------------
Function ACos(rad)
  If abs(rad) <> 1 Then
    acos = PI/2 - atn(rad/sqr(1-rad*rad))
  ElseIf rad = -1 Then
    acos = PI
  End If
End function

#include <stdio.h>
#include <Math.h>
#define PI 3.14159265358979323846
 
double Distance(double lat1, double lon1, double lat2, double lon2, char unit) {
    double deg2radMultiplier = PI / 180;
    lat1 = lat1 * deg2radMultiplier;
    lon1 = lon1 * deg2radMultiplier;
    lat2 = lat2 * deg2radMultiplier;
    lon2 = lon2 * deg2radMultiplier;
 
    double radius = 6378.137; // earth mean radius defined by WGS84
    double dlon = lon2 - lon1;
    double distance = acos( sin(lat1) * sin(lat2) +  cos(lat1) * cos(lat2) * cos(dlon)) * radius; 
    
    if (unit == 'K') {
        return (distance); 
    } else if (unit == 'M') {
        return (distance * 0.621371192);
    } else if (unit == 'N') {
        return (distance * 0.539956803);
    } else {
        return 0;
    }
}
 
 
int main(int argc, char* argv[])
{

lat1 = 41.3879169;
	lon1 = 2.1699187;
	lat2 = 40.4167413;
	lon2 = -3.7032498;

printf("%f", Distance(lat1, lon1, lat2, lon2, 'K'));
    printf("%f", Distance(lat1, lon1, lat2, lon2, 'M'));
    printf("%f", Distance(lat1, lon1, lat2, lon2, 'N'));
}

using System;
 
namespace DistanceCalculatorCs
{
    class Program
    {
        static double Distance(double lat1, double lon1, double lat2, double lon2, char unit)
        {
            double deg2radMultiplier = Math.PI / 180;
            lat1 = lat1 * deg2radMultiplier;
            lon1 = lon1 * deg2radMultiplier;
            lat2 = lat2 * deg2radMultiplier;
            lon2 = lon2 * deg2radMultiplier;
 
            double radius = 6378.137; // earth mean radius defined by WGS84
            double dlon = lon2 - lon1;
            double distance = Math.Acos(Math.Sin(lat1) * Math.Sin(lat2) + Math.Cos(lat1) * Math.Cos(lat2) * Math.Cos(dlon)) * radius;
 
            if (unit == 'K') {
                return (distance);
            } else if (unit == 'M') {
                return (distance * 0.621371192);
            } else if (unit == 'N') {
                return (distance * 0.539956803);
            } else {
                return 0;
            }
        }
 
 
        static void Main(string[] args)
        {
            lat1 = 41.3879169;
            lon1 = 2.1699187;
            lat2 = 40.4167413;
            lon2 = -3.7032498;

Console.WriteLine(Distance(lat1, lon1, lat2, lon2, 'K'));
            Console.WriteLine(Distance(lat1, lon1, lat2, lon2, 'M'));
            Console.WriteLine(Distance(lat1, lon1, lat2, lon2, 'N'));
        }
    }
}

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