Bra Size Calculator – Find Your Band & Cup Size
Just two measurements – underbust and bust – and we’ll give you your estimated US and UK bra size. It’s fast, private, and works for everyone.
Bra Size Calculator
This is your estimated US band and cup size.
Want cup size only, or a different method? See all 14 calculators ↓
What Is a Bra Size, Anyway?
A bra size has two parts: the band (the number) and the cup (the letter). The band wraps around your ribcage, and the cup holds your breasts. Together, they give you a size like 34B or 36D.
The band number comes from your underbust measurement – the part just below your breasts. The cup letter comes from the difference between your bust (fullest part) and your band. Every inch of difference is one cup letter: 1″ = A, 2″ = B, and so on.
How to Measure at Home – Easy Steps
You don’t need a professional fitter. Just follow these simple steps with a soft tape measure (like the kind used for sewing).
📏 1. Underbust
Wrap the tape around your ribcage, right under your bust. Keep it snug but not tight. Take the measurement after you breathe out normally.
Tip: If you get an odd number (like 31), round up to the next even number (32). That’s your band size.
📐 2. Bust
Measure around the fullest part of your bust – usually across the nipples. Keep the tape level and don’t pull it tight. It should sit gently against your skin.
Tip: Take two or three measurements and average them. This gives you a more accurate number.
Now enter both numbers in the calculator above. It will do the math for you and show your size in seconds.
Why Your Bra Size Might Change
Your size can change over time – because of weight changes, pregnancy, or even the brand of bra you buy. That’s why it’s a good idea to measure yourself every few months. Our calculator gives you a reliable starting point every time.
What About Sister Sizes?
Sometimes your usual size is sold out, or a bra fits differently than expected. That’s when sister sizing helps. Sister sizes are bras that hold the same cup volume but have a different band and cup letter.
For example, if you wear 34C, your sister sizes are 32D (smaller band, bigger cup) and 36B (bigger band, smaller cup). If the band feels too tight, try the next sister size up. If it’s too loose, go down.
Need help finding a sister size?
Try Our Sister Size Calculator →US vs UK – What’s the Difference?
The band number is the same in both systems – a 34 is a 34 everywhere. But from cup size D and above, the letters change. For example, a US DDD is a UK E. A US G is a UK F. If you’re shopping from a UK brand, use our conversion tool to make sure you get the right letter.
Why Trust This Calculator?
- It’s free – no sign‑up, no hidden fees.
- It’s private – all calculations happen in your browser, so we never see your measurements.
- It’s accurate – we use the same formula that professional fitters use.
- We update it – our sizing charts are checked regularly to match current brands.
Remember: your result is a starting point. Because every brand and fabric is different, we always recommend trying on a bra before you buy – or ordering a few sister sizes to find the one that feels best.
Ready to get your perfect size?
Head back to the calculator above and enter your measurements right now.
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