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 band measurement to the nearest whole number
If the number is even, add 4 inches
If the number is odd, add 5 inches
Measure your bust size around the fullest part of your breasts
Keep the tape level and not too tight
Subtract the band size from the bust size
Use the difference to find your cup size
1 inch = A cup
2 inches = B cup
3 inches = C cup
4 inches = D cup
5 inches = DD or E cup
Combine the band size and cup size to get your bra size
Recheck your measurements for accuracy