The thing is, once you get to the adult dose. the weight of the person taking it is much less important.
That said, I’ve never known anyone who follows the ibuprofen directions. One or two pills? It’s always been 3 for normal and 4 for prescription strength.
That said, don’t take 8 at once like my aunt did. She died specifically of liver complications from doing that every day for years.
When it comes to cooking frozen food, especially frozen pizza, I usually channel my inner Palin and Go Rogue.
Most, if not all frozen pizzas turn out better (at least to my personal tastes) if the pizza is fully thawed before cooking, which according to the instructions/warnings on the packaging of some frozen pizza brands is courting certain death. I am all about a crisp crust, and for me cooking a thawed pizza gives me a much better finished product than if I play by the rules and cook it from frozen.
I have always been a thrill-seeker, living on the edge, as I have also been known to lather, rinse and NOT repeat.
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Only thing to remember if you try this at home is that if you cook after thawing and/or cook at a higher temp. than what the instructions say, stay close to the oven so you can take it out when it is done to your liking. If you cook it using a timer (for the amount of time it tells you to cook the frozen pizza for) you will have a burned mess, as obviously a thawed pizza will cook a lot faster than a frozen pie would. 
You do now. Two pills, every four hours, maximum six per day. I supplement with tylenol if that’s not cutting it (following those directions, too).
ETA: Someone here mentioned a while ago that pain relief works better if you stop the pain before it gets bad, rather than trying to take it down after it’s already gotten bad, and they were absolutely right.