You can use the Haversine algorithm. Another user has already coded a solution for this:
public double CalculationByDistance(double initialLat, double initialLong,
double finalLat, double finalLong){
int R = 6371; // km
double dLat = toRadians(finalLat-initialLat);
double dLon = toRadians(finalLong-initialLong);
lat1 = toRadians(lat1);
lat2 = toRadians(lat2);
double a = Math.sin(dLat/2) * Math.sin(dLat/2) +
Math.sin(dLon/2) * Math.sin(dLon/2) * Math.cos(lat1) * Math.cos(lat2);
double c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
return R * c;
}
public double toRadians(deg) {
return deg * (Math.PI/180)
}
Source: https://stackoverflow.com/a/17787472/3449528