[prettylily]

If you're comfortable with the size you're currently wearing, then great! But a properly fitting bra should have a band that you can only fit a few fingers under comfortably (you shouldn't be able to pull it far away from your body). Also, different styles will fit different breast types and shapes differently.

Since cup size is relative to band size, D cups are certainly not always big. For some examples, look here: http://www.brabandproject.com/gallery/search/cup/D/