Bra Size Calculator
Enter your underbust and bust measurements and get your size instantly across US, UK, EU, French, Italian, Australian, and Japanese sizing.
Calculate My Bra Size
| Country / System | Band | Cup | Full Size |
|---|
These results are a starting point. Fit varies by brand and style — try an adjacent size if needed. See the Fit Guide for tips on reading the fit.
How the Calculator Works
Two measurements, one straightforward formula.
Measure Underbust
Wrap a tape measure snugly around your ribcage directly under your bust. This number, rounded to the nearest even inch, is your band size.
Measure Bust
Wrap the tape loosely around the fullest part of your chest, keeping it parallel to the floor. This number minus your underbust gives your cup size.
Get All Your Sizes
Enter both measurements above, choose inches or centimeters, and hit Calculate. Your size appears instantly across all 7 major international systems.
About This Calculator
This calculator uses the modern measuring method, which is the approach recommended by most professional bra fitters and lingerie brands today. Your underbust measurement rounded to the nearest even inch becomes your band size. The difference between your bust and underbust determines your cup size.
Unlike older guides that instructed women to add 4 or 5 inches to their underbust, the modern method measures directly. That older approach dates from a time when bras had significantly less stretch. Today's bras use elastic fabrics that accommodate the body without adding extra inches to the calculation.
How Cup Size Is Determined
Once your band size is set, cup size comes from the difference between your bust and underbust measurements. Each inch of difference corresponds to one cup size:
| Difference (inches) | US Cup | UK Cup | EU / FR / JP Cup |
|---|---|---|---|
| Less than 1 | AA | AA | AA |
| 1 | A | A | A |
| 2 | B | B | B |
| 3 | C | C | C |
| 4 | D | D | D |
| 5 | DD | DD | E |
| 6 | DDD | E | F |
| 7 | F | F | G |
| 8 | G | FF | H |
| 9 | H | G | I |
| 10 | I | GG | J |
Note that US and UK cup labels diverge from DD onward, and European, French, and Japanese systems use a simpler alphabetical sequence without double letters. The calculator handles all of these differences automatically.
Already Know Your Size?
If you already have a bra size and need to shop in a different country, the International Bra Size Converter on our home page converts between all seven systems in one click. The Size Chart is also a useful quick-reference for the full band and cup equivalents side by side.
Frequently Asked Questions
Common questions about calculating your bra size.
Wrap a soft tape measure snugly around your ribcage directly under your bust line. Keep the tape level and parallel to the floor all the way around, and breathe normally while you read the number. The tape should be firm but not digging in — you should be able to slide a finger underneath. Write down this measurement in inches or centimeters before taking your bust measurement.
Stand upright, then wrap the tape loosely around the fullest part of your chest. Keep the tape parallel to the floor on all sides. For the most accurate cup measurement, lean forward slightly at about 45 degrees so your breast tissue falls forward naturally before you take the reading. The tape should not be pulled tight — it should rest against your skin without compressing.
No. This calculator uses the modern method, which measures your underbust directly without adding extra inches. The old +4 or +5 method dates from the mid-20th century when bra fabric had very little elasticity. Adding inches compensated for that stiffness. Modern bras use stretchy fabric and construction that fits the body without any adjustment, so measuring directly gives a more accurate result. Most lingerie brands and professional fitters now recommend the modern approach.
A calculated bra size is a reliable starting point, not a guarantee of fit. Individual brands and styles vary in how they cut and grade their bras. Breast shape, projection, and tissue density also affect how a particular bra fits even when the size is technically correct. Think of the result as the size to try first, and go one band or cup size up or down if the fit is slightly off. See our Fit Guide for tips on reading fit once you have a bra on.
Floating between sizes is completely normal. Your measurements may not land exactly on a whole-inch difference, and different brands grade their cups slightly differently. If the calculated cup feels slightly snug, try one cup size up. If it gapes or wrinkles, try one size down. Sister sizing is another option: moving up a band and down a cup (or vice versa) keeps the same cup volume while adjusting the fit around the torso. For example, if 34C feels right in cup volume but the band is too snug, a 36B holds the same volume with a more relaxed band.
Either works, but stay consistent between your two measurements. Many fitters recommend measuring without a bra, or wearing a non-padded, lightly structured bra rather than a padded or push-up style. Heavily padded bras add volume and will cause your bust measurement to read larger than your natural measurement, which can push the result into a larger cup size than you actually need.