Данные

function size_file($dir) {
    global $f_size;
    $dh = opendir ($dir);
    while ($file = readdir($dh)) {
        if($file!="." && $file!="..") {
            $fullpath = $dir."/".$file;
            if(!is_dir ($fullpath))
            {
                $f_size = $f_size + filesize ($fullpath);
            } else {
                size_file($fullpath);
            }
        }
    }
    closedir ($dh);
    return ($f_size);
}

echo size_file('data');