function CalcDirectorySize($DirectoryPath) {

    $Size = 0;
 
    $Dir = opendir($DirectoryPath);
 
    if (!$Dir)
        return -1;
 
    while (($File = readdir($Dir)) !== false) {
 
        // Skip file pointers
        if ($File[0] == '.') continue; 
 
        // Go recursive down, or add the file size
        if (is_dir($DirectoryPath . $File))            
            $Size += CalcDirectorySize($DirectoryPath . $File . DIRECTORY_SEPARATOR);
        else 
            $Size += filesize($DirectoryPath . $File);        
    }
 
    closedir($Dir);
 
    return $Size;
}