There are numerous charts that estimate breast weight based on band/cup size measurements. Google "breast weight" and look at the images. On one chart, I saw my estimated breast weight, a 40B, at 2.9 lbs for both. Seems a little high to me, though, but I don't think mine are quite as full as mature cis-woman. What sorta surprises me is how much tissue is under the arms.
All the best,
--AshleyP