Ask Knickers: How do my measurements translate to a bra size?

This time in Ask Knickers, a confused reader hands over her tape measure and asks for help — how do these measurements translate into a bra size, anyway?

Question:

I’ve been remeasuring myself to find a new bra since my current ones are fitting tight due to pregnancy. My ribcage measures 41″ (add 5″ = 46″ band size) and my bust measures 46″, so does this mean I’m a AA cup?? I’m currently wearing a 40C and spilling out of them (even full coverage bras). I’m not flat-chested in the least and needless to say very confused! What size should I be wearing?

Answer:

Our reader has done everything exactly right — she’s measured over her bust and across her ribcage, the two measurements required for the well-known bra-fitting formula of subtracting bust size from rib size. The problem is, this formula simply isn’t comprehensive enough to be reliable, and can lead to a wildly incorrect size for women — in our readers case, a 46AA! With our tried and not-so-true formula out of the window, how can we find the correct size?

To puzzle out this size we turned to our two favourite bra-sizing experts — Beverly Johnson, the author of the Bra-Makers Manual and an incredible resource to anyone interested in bra-making, and Izzy, the creator of 85b.org, a site dedicated to helping women try to puzzle through the increasing web of bra sizes all over the world. Both women agreed that the two-measurement system was letting our reader down. Izzy elaborated:

It’s evident that an AA cup is not right and this is a major fault with the two-measurement system.

In my experience, this system can work for what I call “petite” sizes – those most commonly found in stores: band sizes from 32 to 36 and cup sizes from AA to C or perhaps D. But even in these cases these two measurements may not be sufficient.

Beverly theorised that our reader’s recent pregnancy could be creating the false measurement, offering:

She doesn’t say whether she is still pregnant, or whether it is recent, but in any case, the ribs may have expanded and not gone back down to their former size. This is making her rib cage bigger, so when the measuring is done, the difference between the rib cage and the full bust is actually very little, therefore a “false size” of 46AA is showing up.

She doesn’t mention if it is the band and cups that are too tight, or just the cups. If it is just the cups that are compressing, I would go into a 40D, or DD if they are really tight. However, if the band is tight as well as the cups, going into a 42C would give her a band increase but only a 1/2 size increase in the cup. Going to the 40D would give her a full cup size of 1/2″ and might solve the problem.

The reality is that no quick and easy formula can account for the incredible variety of women’s shapes and sizes, so measurements can only be judged as a starting point for fitting. While as a first step our reader can try going to a larger cup size, Izzy, Beverly and myself all agree that the best solution is for our reader to be professionally fitted. An experienced fitter will be able to help her experiment with a variety of types of bras and sizes, which is the only real way to guarantee a good fit. There’s always a great bra-fitter in every town, you just have to find her — just stay away from the big chain lingerie stores and look for an older boutique, or try one of the larger department stores with experienced staff. You can also read up more on bra-sizing with our Top Five Bra-Sizing Myths, and over at Beverly’s blog where she explains the craziness that is band sizing.