What is a Sister Size? | ZeroBra Glossary
Understanding Sister Sizes
Sister sizes are bra sizes that have the same cup volume but different band sizes. For example, if you wear a 34B, your sister sizes would be 32C and 36A – all offering the same cup capacity with varying band fits.
How Sister Sizes Work
The concept is based on bra mathematics: when you go up one band size, you go down one cup size to maintain the same cup volume, and vice versa. This happens because cup size is relative to band size. A C cup on a 32 band is smaller than a C cup on a 36 band.
Here's a simple example:
- 32C = 34B = 36A (same cup volume)
- 34D = 36C = 38B (same cup volume)
- 36DD = 38D = 40C (same cup volume)
Why Sister Sizes Matter for Your Comfort
Understanding sister sizes can be a game-changer for your bra shopping experience. If your usual size feels slightly off – maybe the band is too tight or too loose – sister sizes offer alternatives without compromising on cup fit. This is especially helpful when shopping online or when your preferred size is out of stock.
Sister sizes also help you fine-tune your fit based on different bra styles. A bra top might fit differently than a traditional underwire bra, so knowing your sister sizes gives you more options to find the perfect fit.
Who Should Consider Sister Sizes?
Sister sizes work wonderfully for women who:
- Fall between standard sizes
- Experience size fluctuations due to weight changes or hormonal cycles
- Need different fits for different activities (tighter band for gymwear, looser for everyday comfort)
- Have trouble finding their exact size in stock
Tips for Using Sister Sizes
Remember that while cup volume remains the same, the shape and support will change slightly. A smaller band with larger cup letter will give more support, while a larger band with smaller cup letter offers more comfort. For nightwear and lounging, you might prefer the comfort of a larger band, while for active days, a snugger band provides better support.