Wear a non-padded bra or no bra
Use a soft measuring tape
Measure your band size
Wrap the tape snugly around your ribcage, directly under your bust
Keep the tape level and parallel to the floor
Round the 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
Wrap the tape around the fullest part of your bust
Keep the tape level and not too tight
Round the measurement to the nearest whole number
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
6 inches = DDD or F cup
Try on the calculated size
Adjust the band or cup size if needed
Recheck measurements regularly