Sister Sizing and Bra Fitting Methods
Forget adding a mysterious four inches to your band size, or measuring near your armpit. The rib cage method is the accurate, straightforward way to find a bra that actually fits.
Why Accurate Measurement Matters
A bra that fits well can improve your comfort, support, and confidence. A misfitting bra, on the other hand, can cause real discomfort, back pain, and poor posture.
The Rib Cage Method, Step by Step
You'll need a soft measuring tape, a mirror, and your best-fitting non-padded, non-wired bra.
- Measure your band size. Wrap the tape snugly around your ribcage, directly under your bust. The number you get is your band size - no adjustment needed.
- Skip the armpit. Measuring higher up, near the armpit, consistently leads to an oversized band and an ill-fitting bra.
- Measure your bust size. Wrap the tape around the fullest part of your bust.
- Find your cup size. Subtract your band size from your bust size. Each inch of difference is one cup size: 1 inch is an A cup, 2 inches a B cup, 3 inches a C cup, 4 inches a D cup, and so on.
That's it - no adding four inches, no guesswork. Just two measurements and simple subtraction.
What Is Sister Sizing?
Ever felt like nothing quite fits when bra shopping - too big, too small, but never quite right? That's where sister sizing comes in. Many brands offer a limited range of sizes, so instead of stocking every combination, they rely on sister sizing: a 34B and a 32C, for example, share roughly the same cup volume, just distributed across a different band. It lets a brand fudge a fit using what's already on the shelf, rather than truly carrying your size.
Sister sizing can work as a stopgap, but it's not a substitute for knowing your actual band and cup size - which is exactly what the rib cage method gives you.
Why So Many Women Wear the Wrong Size
Roughly 8 out of 10 women wear the wrong bra size - largely because of inconsistent measuring methods across the industry. Without a clear, standardized approach, it's easy to end up guessing, and guessing rarely lands on the right fit. Ill-fitting bras aren't just uncomfortable; they can contribute to shoulder and back pain and poor posture over time.
Teaching the Next Generation
Ending this cycle starts with education. Teaching young women the fundamentals of accurate bra sizing, paired with body positivity and confidence, sets them up to feel comfortable and supported for life - not just for one bra purchase.
BRABAR's Approach
At BRABAR, our mission is to give women, teens, and tweens the knowledge and the products to find a bra that actually fits. That means standing behind the rib cage method, offering real band sizes from 28 to 38 with cups A through DDD/F, and building products around real bodies rather than a one-size-fits-most guess.
For young women in particular, an accurately measured first bra sets the tone for how they think about their bodies going forward - comfort and support first, not confusion.
Use BRABAR's Fit Guide and Bra Size Calculator to find your real band and cup size, and explore the full BRABAR collection once you know your fit.
