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 |
|---|
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.
Short, practical answers to the questions people ask most about measuring and fitting. For deeper dives, see how to measure, sister sizes, and the full size chart.
Measure two things with a soft tape. First, your underbust: wrap the tape snugly around your ribcage directly under your bust, level and parallel to the floor — this gives your band size. Second, your full bust: wrap the tape around the fullest part without compressing. Enter both numbers into the calculator and it returns your band, cup, and international sizes instantly. The difference between the two measurements determines the cup letter. Full walkthrough: how to measure your bra size.
Sister sizes are bra sizes that share the same cup volume but have different band sizes. For example, 34C, 32D, and 36B are all sister sizes — the cup holds the same amount, but the band is tighter or looser. This helps you find a better fit when your usual band size isn't quite right. See sister sizes explained.
US and UK band sizes use the same numbers, but cup sizes differ after D (US DD equals UK DD, but US DDD equals UK E). EU sizes use centimeter-based bands (e.g., US 34 equals EU 75) and a simpler cup progression. Use the international converter or the bra size conversion chart for instant, accurate conversions across US, UK, EU, FR, AU, and JP.
A band that rides up usually means it is too loose. The band provides most of a bra's support, so it needs to be snug. Try going down one band size and up one cup size (a sister size swap) to maintain the same cup volume with a firmer band.
The band does most of the work — roughly 80% of a bra's support comes from a snug band, not the straps. If the band is wrong, nothing else fits correctly: straps slip, the centre lifts, and the wire sits in the wrong place. Fit the band first, then adjust the cup. More on this in band vs cup.
The cup letter is not an absolute volume — it represents the difference between your full bust and your underbust. Each inch of difference is roughly one cup letter: about 1 inch is an A, 2 inches a B, 3 inches a C, and so on. Because it is a difference, the same letter is a different physical size on every band — a 32C cup is smaller than a 38C cup.
Re-measure whenever your weight changes by more than a few pounds, after pregnancy or breastfeeding, around menopause, or simply once a year. Bra size is not fixed — see why bra size changes — and a band also stretches with wear, so a size that fit a year ago may not fit today.
BraCalc uses the standard underbust-and-difference method that bra fitters use, so it gives an accurate starting size for most people. Real bras vary by brand, cut, and material, so treat the result as the centre of a range — try your calculated size plus its two sister sizes. All calculations run in your browser; nothing is sent anywhere or stored on a server.