Bra size is a letter (cup size) followed by a number (size). Pass the tape around the chest under the armpits and over the shoulder blades, around the back. The difference between the waist and chest size will be the size of the cup. A 1 inch, B 2 inches, C 3 inches or or D 4 inches...
Triangle or push-up bras without underwire will suit smaller breasts. For good support of the strongest breasts, opt for a half-cup bra.
A bra must fit well to be comfortable, the size has no pressure points, the breasts fit well through the cup. Should be firm without being too tight under the bust.