Wear an unpadded bra or no bra
Measure your band size by wrapping a tape measure snugly around your ribcage, directly under your bust
Round the band measurement to the nearest whole number
Measure your bust size by wrapping the tape measure around the fullest part of your breasts
Keep the tape level and not too tight
Subtract the band measurement from the bust measurement
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
Check both breasts and use the larger measurement if they differ
Recheck measurements for accuracy