Wear an unpadded bra or no bra
Measure your band size around your ribcage, directly under your bust
Keep the measuring tape snug and level
Round the underbust measurement to the nearest whole number
If the number is even, use it as your band size
If the number is odd, round up to the next even number
Measure your bust size around the fullest part of your breasts
Keep the measuring tape level and not too tight
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 by making sure the band is firm and the cups fully contain the breasts
Re-measure if the bra feels too tight, loose, or gappy