$base_dir = __DIR__; // Absolute path to your installation, ex: /var/www/mywebsite
$doc_root = preg_replace("!{$_SERVER['SCRIPT_NAME']}$!", '', $_SERVER['SCRIPT_FILENAME']); # ex: /var/www
$base_url = preg_replace("!^{$doc_root}!", '', $base_dir); # ex: '' or '/mywebsite'
$base_url = str_replace('\\', '/', $base_url);//On Windows
$base_url = str_replace($doc_root, '', $base_url);//On Windows
$protocol = empty($_SERVER['HTTPS']) ? 'http' : 'https';
$port = $_SERVER['SERVER_PORT'];
$disp_port = ($protocol == 'http' && $port == 80 || $protocol == 'https' && $port == 443) ? '' : ":$port";
$domain = $_SERVER['SERVER_NAME'];
$full_url = "$protocol://{$domain}{$disp_port}{$base_url}"; # Ex: 'http://example.com', 'https://example.com/mywebsite', etc.
source:
http://blog.lavoie.sl/2013/02/php-document-root-path-and-url-detection.html