Wear a non-padded bra or no bra
Measure your underbust snugly to find your band size
Measure around the fullest part of your bust
Subtract the band measurement from the bust measurement
Use the difference to determine the cup size
1 inch difference = A cup
2 inches difference = B cup
3 inches difference = C cup
4 inches difference = D cup
5 inches difference = DD or E cup
6 inches difference = DDD or F cup
Try on bras in the calculated size to confirm fit
Check that the band sits level and snug
Check that the cups fully contain the breasts without spillage or gaps