To use the table of English bra sister sizes, first determine your usual bra size, which is typically based on your underbust measurement (rib cage) and your overbust measurement (bust).
If you find that the bra you’re trying on doesn’t fit in the band, you can use the sister sizes to find a better-fitting bra that has the same cup volume but a different band size.
For example, if you usually wear a 32C but find that the band feels too tight, you can look at the sister sizes to find other options. You could try a 34B, which has the same cup volume as 32C but with a larger band, or a 30D, which has the same cup volume but with a smaller band.
Remember that as you go up or down in band size, you will need to adjust the cup size accordingly to maintain the same volume. If you go up in band size, you should go down in cup size, and if you go down in band size, you should go up in cup size.
Using sister sizes can be a helpful tool when trying to find the right bra size and fit, but keep in mind that everyone’s body is different and it’s important to try on bras and experiment with different sizes to find what works best for you.