These calculators seem to be more directed at the "hollywood" world of whats big and whats small. Small being less than like size 0, and big being oh yeah know like size 2... Watch America's Next Top Model, they have "plus size" models who are literally size 5 i think... i would love to be size 5! And they don't say that the girls are too skinny until you can see their ribs, and shoulder bones. The "proper size" is maybe a size 0, 1 or 2 (Max.)
back in the real world every one is themselves. So what if you are a size 10? that's not fat, or if you are a size 0, and not malnourished, thats who you are. Unless your weight is bad for your health, it doesn't really matter what size you are.