The cup size is determined by the difference between chest circumference and thorax circumference (measured below the breast, rounded to 5 centimeters). A difference of 13 centimeters stands for cup size A, 15 centimeters for cup size B, 17 centimeters for cup size C, and so on.
Your underbust circumference is for example 75 centimeters. If you now have a chest circumference of 88 centimeters (measured at the widest part) you have cup size A, in case of a chest circumference of 90 centimeters you have cup size B, in case of 92 centimeters C, and in case of 94 centimeters D.
An augmentation of your breast by autologous fat transfer by one cup size corresponds to an increase of the chest circumference of 2 centimeters.
DDr. Heinrich, MD