To accurately estimate breast size, specific personal measurements are needed, such as chest circumference under the breasts (band size) and the fullest part of the breasts (bust size). Breast size is typically expressed in bra sizes, which combine a band size (number) and a cup size (letter). If you provide your underbust and bust measurements in inches or centimeters, I can help calculate your estimated bra size or breast volume. Without those, it's not possible to determine breast size.