I hear from many people that a 75B, say, is the same as an 80A and that I’m better off with a small chest size and a larger cup than vice versa. Is that right? 

In the industry jargon this is called cross sizing. Unfortunately, the answer is a little more complicated than the question might suggest. 

To get one thing out of the way: a 75B is not the same as an 80A. In the 75B, the chest circumference under the cups is 75 cm. It is suitable for women with a chest measurement of 73-77 cm. In the 80A, the chest circumference under the cups is 80 cm. It suitable for women with a chest measurement of 78-82 cm. 

The letter is an indication of the breast volume and has consequences on (a) the depth of the cup and (b) the breadth of the wiring under the cup. The wiring on the 80A bra is therefore not the same as the wiring on the 75B. The breast volume may be about the same for both, but that volume is not distributed in the same way with respect to the shape of the breast and the size of the body. 

For Marie Jo we closely study fabric elasticity to establish the chest measurement. The elasticity of a 75 for instance is checked and tested so that it is perfectly suited to women with a chest measurement of 73-77 cm. That means that we have no need to cross size our brands. On the contrary, we are against it. 

Manufacturers of cheap lingerie often use cross sizing, because they lack the know-how to offer a good fit in the different sizes. They do not want to make the substantial investments to develop this know-how either. 

There is only one way to know for sure and that is having yourself fitted by the lingerie specialist in your specialist lingerie store. Be sure to try on plenty of different types of bras in the various sizes. You will be rewarded, we assure you.