well there you go. If you want 100% coverage on the roof look into about 20-25 sq feet. Should be pretty close to what you need. I'm just getting the large flat sections since I won't run more than a single 12". I'm putting American Bass Deadener in mine. 10 Sq Feet should be enough for me.
buy a 40 square foot pack and do 125% coverage lol. pretty sure with good deadener you should only need 50% coverage ya meen. but if I tear my head liner out I'm doing at least 100% lol