View file sys/inc/functions/size_file.php

<?php 

function size_file($bytes = 0)
{
    $symbols = array('B', 'Kb', 'Mb', 'Gb', 'Tb', 'Pb', 'Eb', 'Zb', 'Yb');
    $exp = floor(log($bytes) / log(1024));

    return sprintf('%.2f ' . $symbols[$exp], ($bytes / pow(1024, floor($exp))));
}