Bra size calculator
The basics
Why your bra size matters
A well-fitting bra improves posture, reduces discomfort, and makes clothes fit better. Yet studies suggest the vast majority of women are wearing the wrong size — often because they've never been properly measured, or because sizing varies so much between brands and countries.
An ill-fitting bra doesn't just feel uncomfortable — it can cause real physical problems. Straps that are too tight dig into shoulders and restrict circulation. A band that rides up means the bra isn't doing its job of providing support from below. Cups that are too small push breast tissue to the sides, while cups that are too large leave the bra gaping and shapeless.
The right fit means all four of the following:
- The band sits firm and level all the way around your body
- The cups contain all breast tissue without overflow or gaps
- The straps rest gently on the shoulders without digging in
- The underwire, if present, sits flat against the ribcage and chest wall
Getting these four things right starts with accurate measurements.
Step by step
How to measure yourself
You only need a soft measuring tape and about two minutes.
Stand straight and breathe normally. Wrap the tape snugly around your ribcage, directly beneath your bust. Keep the tape parallel to the floor and take note of the number in inches. This is your raw band measurement.
Lean slightly forward so your breast tissue falls naturally. Wrap the tape loosely around the fullest part of your bust — usually across the nipple line. Keep the tape level and don't pull it tight. Record this number.
That's it. Enter both numbers into the calculator to get your size.
The maths
How bra sizes are calculated
Your band size is derived from your underbust measurement. In US and UK sizing, the raw measurement is rounded up to the nearest even number — so 31 inches becomes a band size of 32, and 33 becomes 34.
Your cup size is calculated from the difference between your bust and band measurements:
| Difference | Cup size |
|---|---|
| 1 inch | A |
| 2 inches | B |
| 3 inches | C |
| 4 inches | D |
| 5 inches | DD |
| 6 inches | DDD / E |
The larger the difference, the larger the cup. The calculator handles all of this automatically.
Around the world
International sizing differences
Bra sizing is not universal. The same physical measurements produce different size labels depending on where the bra was made. This calculator converts your size into all major international standards automatically.
🇺🇸 US & 🇬🇧 UK
Same cup letters, but band sizes calculate slightly differently. UK sizing tends to run truer to the raw measurement.
🇩🇪 EU
Adds approximately 15–16 to the US band number. A US 34 becomes EU 70 or 75 depending on the brand.
🇫🇷 FR / 🇪🇸 ES
Adds around 15 to the band, giving sizes in the 80–100 range for most women.
🇮🇹 IT
Uses a numbered scale from 1 upward, with 1 corresponding roughly to a US 28 band.
🇦🇺 AU / 🇳🇿 NZ
Subtracts around 16 from the US band number, landing in a 10–18 range similar to clothing sizes.
Shopping internationally? Always check which sizing system a brand uses before ordering. A size label alone means nothing without knowing the country standard behind it.
Expert advice
Tips for a better fit
Sizing is a starting point, not a verdict. Bras stretch over time, so if you're between sizes, it's worth trying both. Always fasten a new bra on the loosest hook — this leaves room to tighten as the fabric relaxes with wear.
If a bra fits well in the band but not the cup, go up or down a cup size first. If the band feels wrong, adjust the band size before changing the cup.
Cup size is also relative to band size. A 34C and a 36B hold roughly the same volume of breast tissue — these are called sister sizes. Knowing yours gives you more flexibility when shopping:
Remember: A perfect fit should feel comfortable from the moment you put it on. If you're constantly adjusting throughout the day, it's a sign something isn't quite right with the size or style.