Studies on bra fitting consistently find that a large majority of people are wearing the wrong size — usually a band that's too big and a cup that's too small. Getting this right starts with two simple measurements.
How to Measure Band Size
Wrap a soft tape measure snugly around the ribcage, directly underneath the bust, keeping the tape level and parallel to the floor. Round to the nearest whole number. If the result is an odd number, round up to the nearest even number — most bras are sized in even-numbered bands.
How to Measure Cup Size
Measure around the fullest part of the bust, again keeping the tape level. Subtract the band measurement from this number — the difference in inches maps to a cup letter:
| Difference (in) | Cup Size |
|---|---|
| 1 | A |
| 2 | B |
| 3 | C |
| 4 | D |
| 5 | DD/E |
| 6 | DDD/F |
US to UK to EU Conversion
| US Band | UK Band | EU Band |
|---|---|---|
| 32 | 32 | 70 |
| 34 | 34 | 75 |
| 36 | 36 | 80 |
| 38 | 38 | 85 |
| 40 | 40 | 90 |
Cup letters generally align between US and UK, though European cup sizing (using letters like B, C, D) sometimes runs one size larger in equivalent fit — try before assuming an exact match.
Why a Professional Fitting Still Helps
Self-measurement is a reliable starting point, but band-cup proportions vary meaningfully between brands and styles. A one-time professional fitting (available free at many department and lingerie stores) helps calibrate your self-measurement against real-world fit, after which you can shop online with much more confidence.
The Bottom Line
Two tape-measure readings get you most of the way to an accurate bra size. Re-check annually or after any major body change, and don't be afraid of an in-store fitting if your self-measured size doesn't feel quite right.