Wear a non-padded bra or no bra
Measure your underbust snugly to get your band size
Round the underbust measurement to the nearest whole number
Measure around the fullest part of your bust to get your bust size
Subtract the band size from the bust size
Use the difference to find the cup size
1 inch = A cup
2 inches = B cup
3 inches = C cup
4 inches = D cup
5 inches = DD or E cup
6 inches = DDD or F cup
Combine band size and cup size to get your bra size
Example: 34 band and 3-inch difference = 34C