Used to be a bra fitter. So you subtract your cup size from your band size. In your case, 32-25 is seven. Then, you go down the alphabet 7 times. A B C D E F —> G <—. You are technically a 25G. Unfortunately, 25 is an odd number, so you are in-between band sizes. You would round 25 to the nearest even number, which is 26. When you go UP a band size, you go DOWN a cup size. So, your sister size is 26F.+