Many bra fitting guides and calculators will tell you to add four or five inches to your underbust measurement, but this is not correct.. Bras are designed to fit like this so that you can tighten the band as the elastic starts to wear out. They have a limited range of sizes and tend to fit us at whatever come closest to what they offer! )If you need to measure on your own, hold the tape measure low and level around your rib cage. If they are too small, or even if they seem to fit ok, try on a bigger cup size as well to double check. In fact, many women who take the Pill, which contains estrogen, for birth control often experience as a side effect the feeling of breast fullness caused by water retention.If you wear a cup size larger than D, it is good to understand how many D ' s you actually are, so that you can do the conversion according to manufacturer. You can also buy one of those bra hook extenders, and sew it onto your bra band, behind the rows of eyelets ( basically in reverse