function display_filesize($filesize){
    
    if(is_numeric($filesize)){
    $decr = 1024; $step = 0;
    $prefix = array('Byte','KB','MB','GB','TB','PB');
        
    while(($filesize / $decr) > 0.9){
        $filesize = $filesize / $decr;
        $step++;
    } 
    return round($filesize,2).' '.$prefix[$step];
    } else {

    return 'NaN';
    }
    
}