Breasts in Anime and Manga

Buxom Is Better usually runs from "Large" and above, with the divide between Realistic and Absurd types seemingly occurring between low-end and high-end Very Large; mid-level Bakunyuu itself is pretty much a grey area that  can go either way. On the other hand, Gag Boobs - by strict defintion - can not go below mid-level-to-high-end Average.

See also Useful Notes on Bra Sizes.

If you want to see a good visual aid of what this chart would look like, from smallest to largest, see the below picture: