Smart Pop 94% Fat Free Butter Popcorn w/ Pop-up Bowl

I have to admit that the nutrition facts of popcorn have always confused me! Perhaps it's just that I've never measured unpopped amounts against popped amounts, but it always seemed that caloried "disappeared" (really just due to unporportional unpopped vs. popped serving sizes I'm sure). Now that I'm dieting, I'm paying more attention to these things. On the nutrition facts on the package, it gives both the unpopped and popped nutrition facts. It goes further to define that 3 tbs of unpopped popcorn is approximately 7.5 cups of popped popcorn. It also says that there are two 3 tbs unpopped servings in each bag, which would mean that there 15 cups of popped popcorn which I can tell you is definitely not the case! There's maybe 7-8 cups popped but that's a big difference from 15 cups (the bag was packed full, it's not like half the kernals didn't pop). So which is better to go by? To be conservative, I'd use the unpopped calories and figure each bag is two servings and try to estimate from there or is it better to actually measure out how many cups of popped popcorn there are and use that?

-Janice