Sister sizes are groups of bra-size equivalents that are related by cup volume, regardless of the band size and cup letter. For example, a 36B and a 38A are technically the same size because the cup volume is the same. However, a 36A and a 38A are not equivalent sizes.
So how does sizing work if I need to go bigger or smaller?
Easy! Just follow these three simple rules to figure out your sister size:
- The band fits, but your cups don’t: Go up or down a cup letter keeping the same band size. (Example: If the 32A feels small in the cups, go up to a 32B. If the 32A feels big in the cups, go down to a 32AA)
- Your cups fit, but the band doesn’t: Adjust both your band size and cup letter. If the band feels small, go up a band size but down a cup letter. (Example: 32A band feels small, go up a band to a 34 but down a cup letter for a 34AA) If the band feels big, go down a band size but up a cup letter. (Example: 32A band feels big, go down a band to a 30 but up a cup letter for a 30B)
- Neither cup or band fit: Go down a band size if they’re both too big, or go up a band size if they’re both too small. Fun fact: the cups will naturally adjust with your band so you don’t need to adjust the cup size here. (Example: If the 32B was too small, try the 34B. If the 32B was too big, try the 30B)
This is confusing for mostly everyone but don’t worry! Check out our handy chart below.