Human Readable File Size with PHP

gistfile1.php

<?php
# http://jeffreysambells.com/2012/10/25/human-readable-filesize-php
function human_filesize($bytes, $decimals = 2) {
    $size = array('B','kB','MB','GB','TB','PB','EB','ZB','YB');
    $factor = floor((strlen($bytes) - 1) / 3);
    return sprintf("%.{$decimals}f", $bytes / pow(1024, $factor)) . @$size[$factor];
}

echo human_filesize(filesize('example.zip'));

Another version, eliminates needless count() units will always be 5, ** operator, optional unit output, reworked array for determining decimals by the factor

function human_bytes(int $bytes, $u = false): string {
    if ($bytes < 1) return 0;

    $units = ['B', 'Kb', 'Mb', 'Gb', 'Tb', 'Pb'];
    $factor = min(floor(log($bytes, 1024)), 5);
    $value = round($bytes / (1024 ** $factor), $factor > 1 ? 2 : 0);

    return $u ? $value . $units[$factor] : $value;
}

Another version, eliminates needless count()

just FYI: count is "free" operation in php, cause array always have its size in internal structure.