Smart displaying of file size - PHP Snippet

This php function will smartly display the file size, instead of displaying the size in bytes, why not display GB, MB, KB or bytes as well.

function file_size($url){ 
    $size = filesize($url); 
    if($size >= 1073741824){ 
        $fileSize = round($size/1024/1024/1024,1) . 'GB'; 
    }elseif($size >= 1048576){ 
        $fileSize = round($size/1024/1024,1) . 'MB'; 
    }elseif($size >= 1024){ 
        $fileSize = round($size/1024,1) . 'KB'; 
    }else{ 
        $fileSize = $size . ' bytes'; 
    } 
    return $fileSize; 
} 
echo file_size('/myfile/image.jpg');