Did you know that your bra size has alternative sizes called sister sizes? Sister sizes are groups of bra sizes with the same cup volume. For example, if you wear a 34C, your sister sizes are 30E, 32D, 36B and 38A.

Here’s an analogy to help you out. Imagine a mountain with a fixed amount of volume. Now imagine the mountain narrows (and ends up being taller) and then imagine the mountain widens (and ends up being shallower). No matter the scenario, the volume remains the same. Get it?

When to use your sister size

So what are some scenarios when you would use your sister sizes?

• When you can't find your regular size
• When your cups fit but your band is too small or too big

Scenario 1:

Imagine you’re in a store and you want to try on your normal 34C size but they’re out of stock. Should you try on a 32C or 36C instead? No, because these are not the correct sister sizes to your normal 34C size. You should try on a 32D or a 36B instead as these are the correct sister sizes. Both these sizes share the same volume as a 34C so it’s worth seeing if either fit.

Scenario 2:

Imagine you’re in a store and you’re trying on a bra in your normal 34C size. The cups fit but the band is too tight. You might think to yourself, “I’ll try on a 36C.” However, this is not the right thought process. If you try on the 36C, you will notice that the bra cups will be too big.

This is because a 36C is not a sister size of your normal 34C. Instead, the correct sister size when your cups fit but your band is too tight is your sister size up which is a 36B.

The same logic applies in a scenario where the cups fit fine but the band is a bit too big. You would try on your sister size down which is a 32D.