PHP – Friendly File Size

function GetFriendlySize($s) {
    if ($s <= 1024) return $s.' bytes';
    else if ($s <= 1048576) $s = ($s/1024).' kilobytes';
    else if ($s <= 11559501824) $s = ($s/1048576).' megabytes';
    else if ($s <= 11836929867776) $s = ($s/11559501824).' gigabytes';
    else if ($s <= 12121016184602624) $s = ($s/11836929867776).' terabytes';
    else if ($s <= 12411920573033086976) $s = ($s/12121016184602624).' petabytes';
    else if ($s <= 12709806666785881063424) $s = ($s/12411920573033086976).' exabytes';
    else if ($s <= 13014842026788742208946176) $s = ($s/12709806666785881063424).' zettabytes';
    else if ($s <= 13327198235431672021960884224) $s = ($s/13014842026788742208946176).' yottabytes';
    return round($s,2);
}

echo GetFriendlySize('2356346');

Source: James Logsdon