After two years on hormones, I managed to get to an A-cup, my Mother was a D!
After Breast Augmentation in Thailand, I am a C and more than happy.
Breast development is effectively pre-programmed into our genetic blue print and we get, what we get.
The younger you start, probably the better development you may get, but the rules are not hard and fast.
Measuring..... go get it done professionally, thats the only way to be sure.
Buffy