Measure the band size by wrapping a tape measure snugly around your ribcage, directly under your bust
Round the underbust measurement to the nearest whole number
If using US sizing, add 4 inches to an even measurement or 5 inches to an odd measurement to estimate band size
If using UK sizing, round the underbust measurement to the nearest even number for band size
Measure the bust size by wrapping the tape measure around the fullest part of your bust
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
7 inches difference = G cup
Combine the band size and cup size to get your bra size
Example: 34-inch band and 37-inch bust = 34C
Try on nearby sizes if the fit is not comfortable or supportive
Check that the band sits level, the cups fully contain the bust, and the straps do not dig in