Wear a non-padded bra or no bra
Measure your band size by wrapping a tape measure snugly around your ribcage under your bust
Round the underbust measurement to the nearest whole number
Measure your bust size by wrapping the tape measure around the fullest part of your breasts
Round the bust measurement to the nearest whole number
Subtract the band size from the bust size
Use the difference to determine 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
7 inches difference = G cup
Check the fit and adjust for brand differences if needed