Wear an unpadded bra or no bra
Measure your ribcage directly under your bust
Keep the measuring tape snug and level
Round to the nearest whole number
Measure around the fullest part of your bust
Keep the tape level across your back
Do not pull the tape too tight
Round to the nearest whole number
Subtract the underbust measurement from the bust measurement
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
Combine the band size and cup size to get your bra size
Try on the size to check fit
Adjust band and cup size if needed