What Is Sister Sizing (Simple Guide)
Updated: Jul 18
Most women are surprised to learn that they don’t have just one bra size.
In reality, there are a few “sister sizes” — nearby sizes that can fit just as well depending on the bra’s style, fabric, and how your body feels that day.
Sister sizing became widely known in the 2010s as online bra shopping grew.
Women needed a simple, flexible way to adjust fit without trying anything on — and this idea resonated because it felt reassuring and intuitive.
Sizing is flexible — your comfort comes first.
How Sister Sizes Work (Simply)
If the band feels too tight:
Go up one band size and go down one cup letter.
(For example, if you wear a 34B, your sister size is 36A).
If the band feels too loose:
Go down one band size and go up one cup letter.
(For example, if you wear a 34B, your sister size is 32C).
That's it. Simple as that!
Why Sister Sizes Matter
Every body is different, and even your own body can change from week to week.
Sister sizes give you the flexibility to adjust and find what feels most comfortable.
A More Comfortable Way to Find Your Fit
Think of sister sizes as your quiet safety net.
They make bra shopping easier, kinder, and more adaptable — especially when shopping online. Instead of feeling limited to one size, you have options. You have room to adjust.
And most importantly, you have a better chance of finding a bra that truly feels right for your body.
A Gentle Place to Start
If you’re unsure where to begin, a simple starting point can help.
