PHP function to get the folder size including subfolders

convert_bytes.php

function sizeFilter($bytes)
    {
        $label = array('B', 'KB', 'MB', 'GB', 'TB', 'PB');

        for ($i = 0; $bytes >= 1024 && $i < (count($label) - 1); $bytes /= 1024, $i++) ;

        return (round($bytes, 2) . " " . $label[$i]);
    }

foldersize.php

<?php

function folderSize ($dir)
{
    $size = 0;

    foreach (glob(rtrim($dir, '/').'/*', GLOB_NOSORT) as $each) {
        $size += is_file($each) ? filesize($each) : folderSize($each);
    }

    return $size;
}

large_folder.php

$f = './path/directory';
    $io = popen ( '/usr/bin/du -sk ' . $f, 'r' );
    $size = fgets ( $io, 4096);
    $size = substr ( $size, 0, strpos ( $size, "\t" ) );
    pclose ( $io );
    echo 'Directory: ' . $f . ' => Size: ' . $size;