Band Size Calculator – Find Your Bra Band Number
Enter your underbust measurement below, and we’ll give you your band size – the number in your bra size (like 34, 36, or 38). It’s fast, private, and works for everyone.
Band Size Calculator
Your estimated band size is 34.
Now that you have your band, find your full bra size with the Bra Size Calculator or get your cup letter with the Cup Size Calculator.
What Is a Band Size?
Your band size is the number in your bra size – like 34, 36, or 38. It comes from your underbust measurement, which is the circumference of your ribcage just below your breasts. The band is the part of the bra that wraps around your body and does most of the heavy lifting – about 80% of the support comes from the band, not the straps.
That’s why getting your band size right is so important. A band that's too tight can dig in and be uncomfortable. A band that's too loose won't give you enough support, and the straps will have to work too hard.
How to Measure Your Band Size
1. Use a Soft Tape Measure
Take a flexible tape measure – like the kind used for sewing. Make sure it’s not stretched or twisted.
2. Stand Up Straight
Keep your feet flat, shoulders relaxed, and arms at your sides. Breathe out normally before measuring.
3. Measure Just Below Your Bust
Wrap the tape around your ribcage, right under where your breasts start. Keep it snug but not tight – it should feel firm but comfortable.
4. Round to the Nearest Even Number
If your measurement is 31″, round up to 32″. If it’s 33″, round up to 34″. Bra bands come in even numbers (28, 30, 32, 34, etc.).
Enter your underbust measurement in the calculator above, and we’ll do the math for you – giving you your exact band size in seconds.
Why Your Band Size Matters
The band is the foundation of your bra. A properly fitted band sits level across your back, stays in place when you move, and doesn't ride up. It should feel firm but not painful. If you can pull the band more than a few inches away from your body, it's too loose. If it leaves red marks or feels uncomfortable, it might be too tight.
Your band size can also change over time – due to weight changes, muscle gain, or even just different brands. That’s why it’s a good idea to measure yourself every few months.
Band Size vs. Cup Size – What’s the Difference?
Your band size is the number (34, 36, etc.). Your cup size is the letter (A, B, C, etc.). Together, they make your full bra size like 34B or 36D. The band size comes from your underbust, and the cup size comes from the difference between your bust and your band. Both matter – you can't have one without the other.
Sister Sizing – Same Cup, Different Band
If you’re between band sizes, or if your usual band size is sold out, you can try a sister size. Sister sizes have the same cup volume but a different band. For example, if you wear a 34B, your sister sizes are 32C (smaller band, larger cup) and 36A (larger band, smaller cup).
Use our Sister Size Calculator to find your matches.
Got your band size? Now find your cup.
Try the Cup Size Calculator →Why Trust This Calculator?
- It’s free – no sign‑up, no hidden fees.
- It’s private – all calculations happen in your browser – we never see your measurements.
- It’s accurate – we use the same formula that professional fitters use.
- We keep it updated – our charts match current brand sizing.
Remember: your band size is a great starting point. Every brand fits a little differently, so always try on a few styles to find the one that feels best.
Ready to find your band size?
Enter your underbust measurement in the calculator above right now.
Go to Calculator ↑