The time required by the browser to load the page:
Notes: Must be the first thing in the head as soon as scripts are allowed there, as shown. Time will only be approximate as it doesn't include loading of meta data or title, etc. But, these usually take very little time.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/1999/REC-html401-19991224/loose.dtd">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
var begin=new Date().valueOf();
var end=new Date().valueOf();
alert('This page took '+[end-begin]+' milliseconds to load');
Also, this is just the concept. Any particular implementation could, and probably should be a bit different.