Php File Size Converter Function

This code is file size converter function with php.

<?php
function formatSizeUnits($bytes)
    {
        if ($bytes >= 1073741824)
        {
            $bytes = number_format($bytes / 1073741824, 2) .  GB;
        }
        elseif ($bytes >= 1048576)
        {
            $bytes = number_format($bytes / 1048576, 2) .  MB;
        }
        elseif ($bytes >= 1024)
        {
            $bytes = number_format($bytes / 1024, 2) .  KB;
        }
        elseif ($bytes > 1)
        {
            $bytes = $bytes .  bytes;
        }
        elseif ($bytes == 1)
        {
            $bytes = $bytes .  byte;
        }
        else
        {
            $bytes = 0 bytes;
        }

        return $bytes;
};
?>