Bra sizes actually have a 5cm tolerance at the underbust . For this reason each bra has a offers at the fastener which allows you the possibility to adjust the width to suit the individual ly . It is advisable to do up wear the bra in the middle of the clasp adjustability , if your back measurement underbust is exactly the same as the indicated size. If Do you have a smaller back underbust width you should do up close t t he bra at its in the tightest adjustability , with a larger back underbust width the bra can might be done up at its loosest. worn in the largest adjustability.