Er, that tells me 1. Every time. Exactly as I expected.
In general terms:
You could turn output buffering off, generate a page, and see how much data you've buffered. That'll give you the HTML content.
If this is for testing purposes, however (and you wouldn't want the overhead in a production environment), the obvious solution is to just send it to a suitable browser (eg. IE5+, Netscape6+ or Mozilla) and then save the complete page and then look at filesizes of the result.