Wear a non-padded bra or no bra
Measure your band size around your ribcage, directly under your bust
Keep the tape snug and level
Round to the nearest whole number
Measure your bust size around the fullest part of your breasts
Keep the tape level and not too tight
Round to the nearest whole number
Subtract your band size from your bust size
Use the difference to find 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
Try on different sizes for the best fit