Two measurements. Every major sizing system. Accurate results in under 10 seconds — with sister sizes and international conversions included.
All you need is a soft measuring tape and 60 seconds. If a calculation comes out feeling wrong, see the guide to common measuring mistakes; for why a long-time size sometimes stops fitting, read when bra size changes.
Wrap the tape snugly around your ribcage, directly under your bust. Keep it level and breathe normally.
Wrap the tape around the fullest part of your bust without compressing. Keep it parallel to the floor.
Enter both numbers below. BraCalc instantly calculates your size across 6 international systems.
Same cup volume, different band — try these if your usual size isn't quite right.
Sizes in each row share the same cup volume. Move right for a looser band, left for a tighter one. Why sister sizes work walks through the underlying logic.
| Volume | 28 | 30 | 32 | 34 | 36 | 38 | 40 | 42 | 44 |
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Instantly convert between US, UK, EU, FR, AU, and JP bra sizing systems.
Tap any issue you're experiencing to see what's causing it and how to fix it. For the underlying logic, see band vs cup and the bra styles guide.
The back of your bra creeps upward throughout the day, forming an upside-down U shape.
The fix: Your band is likely too loose. Try going down one band size and up one cup (e.g., 36C → 34D). The band should sit level and parallel to the floor.
No matter how tight you adjust them, the straps slide off your shoulders.
The fix: This is often a band issue, not a strap issue. If the band is too big, it can't anchor the straps. Try a smaller band size, or look for styles with a center-pull or J-hook strap.
There's visible space or wrinkling at the top or sides of the cups.
The fix: Try going down a cup size. If only the top gaps, try a demi or balconette style instead. Shape mismatch is often the cause, not just size.
The underwire sits on breast tissue, pokes under the arms, or leaves red marks.
The fix: The cup may be too small, pushing the wire onto tissue. Go up a cup size. If the wire pokes at the center, you may need a wider-set wire style.
Breast tissue spills over the top edge of the cup, creating a double-bump effect.
The fix: Go up one cup size. If the band fits well, only change the cup. Full-coverage and minimizer styles also help contain tissue better.
The center piece between the cups lifts away from your sternum instead of laying flat.
The fix: The cups are likely too small. Go up one or two cup sizes until the gore tacks flat against your chest. This is the #1 sign of an incorrect cup size.
Pick a band number to see every cup, with measurements, sister sizes, international conversions, and fit tips for that exact size.