>>60478861D-cups are quite small if you have a small frame
A 28D is the same volume as 30C and the same volume as a 32B. They all are 310 cm^3 or 19 cubic inches is volume, so a little less than a can of coke per each tit. This is with the US system, if we use the japanese system which IIRC we move down a cup size she has a breast volume of 240 cm^3 or 14 cubic inches, quite a bit less, a 23% decrease from the US system