how to find page loading time

copy and paste the following code in top of the pages :

$time = microtime();
$time = explode(' ', $time);
$time = $time[1] + $time[0];
$start_time = $time;

copy and paste the following code in last of the pages :

$time = microtime();
$time = explode(' ', $time);
$time = $time[1] + $time[0];
$finish_time = $time;
$total_time = round(($finish_time - $start_time), 3);
echo 'Page lodaing time '.$total_time.' seconds.'."\n";