Like this post?
Initial response aside, my one thought is... WHY?!?
What would you do if you DID know how you "stacked up" compared to him? It's not like you can run around saying "nyah nyah, I'm bigger than Dad!" Everyone would think your sick. And if it turned out that you were smaller... well then you'll be sorry you found out for sure, wouldn't you?
Also, what do you think your dad's response would be if you actually asked him about this? Chances are good that he's not a nudist, since this wouldn't be an issue then... I can only imagine the poor guy's response wouldn't be terribly favorable. So your only alternative would be to "accidentally" see him sometime. That could lead to some SERIOUS father/son issues!
Seriously, even if your dad is in AWESOME shape - there are just some things you don't need to know about him.