Wear a non-padded bra or no bra
Measure your band size around your ribcage, directly under your bust
Round the band measurement to the nearest whole number
Measure your bust size around the fullest part of your chest
Subtract the band size from the bust size
Use the difference to determine your 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
8 inches difference = H cup
Try on different bra styles to confirm the fit
Check that the band sits level and snug
Check that the cups fully contain the breasts without gaps or spillage