International Bra Sizing Tool
Estimate US, UK, EU, French/Spanish, and Australian bra sizes from your underbust and full-bust measurements.
Your estimated sizes
How to use this Bra Size Calculator
- Measure directly beneath the bust while keeping the tape level and comfortably snug.
- Measure around the fullest part of the bust without compressing the tissue.
- Select inches or centimeters and choose a calculation method.
- Calculate, then compare the five international size labels shown.
For the most useful Bra Size Calculator result, measure twice and use the average. Wear a lightly lined or unpadded bra while measuring, stand naturally, and keep the tape parallel with the floor. If possible, ask another person to confirm the tape position. Measurements taken over bulky clothing usually produce a less reliable estimate.
Bra size formula and band methods
The classic method rounds the underbust to an even inch and adds four inches to estimate the US/UK band. The direct method rounds the underbust itself to the nearest even band. Cup size is estimated from the difference between full bust and the calculated band: approximately one inch per cup step.
Classic band = nearest even underbust + 4 inches.
Cup difference = full bust − band size.
This Bra Size Calculator supports both common approaches. The direct method often gives a firmer band and a larger cup letter because bra volume is shared between band and cup. This relationship is why adjacent “sister sizes” can fit similarly: going down one band usually means going up one cup, while going up one band usually means going down one cup.
Worked example
For a 30-inch underbust and 36-inch full bust, the classic method estimates a 34-inch band. The two-inch bust-to-band difference corresponds to a B cup. The starting result is therefore US 34B and UK 34B, with approximate equivalents EU 75B, FR/ES 90B, and AU/NZ 12B.
International band conversion chart
| US / UK | EU | FR / ES | AU / NZ |
|---|---|---|---|
| 30 | 65 | 80 | 8 |
| 32 | 70 | 85 | 10 |
| 34 | 75 | 90 | 12 |
| 36 | 80 | 95 | 14 |
| 38 | 85 | 100 | 16 |
| 40 | 90 | 105 | 18 |
| 42 | 95 | 110 | 20 |
The Bra Size Calculator displays practical international equivalents. Cup lettering diverges after D. For example, the calculator maps US DD/E to UK DD and EU E, while later US and UK sequences differ further. Always confirm both the band and cup on the retailer’s chart.
How to check the fit
After using the Bra Size Calculator, confirm the result with a fit check. A suitable band should sit level around the torso and feel supportive on the loosest hook when new. The center gore should rest close to the chest, the underwire should surround the breast tissue, and the cups should not wrinkle or spill. Straps add stability but should not carry most of the weight.
If the band rides upward, try a smaller band and increase the cup to preserve similar volume. If the band feels correct but the cup cuts in, increase the cup. If the cup wrinkles, decrease it. Shape, wire width, cup depth, fabric, and style can affect fit even when the printed size is identical.
Accuracy, privacy, and limitations
This Bra Size Calculator runs in your browser; the measurements are not sent to our server by the calculation. Results are educational estimates rather than a professional fitting. Bodies are asymmetric, measurements can change, and brand construction varies. Recheck after major weight change, pregnancy, or whenever fit becomes uncomfortable.
A Bra Size Calculator cannot remove every brand difference. International labels are practical conversions, not proof that garments have identical dimensions. The ISO body-measurement guidance explains standardized approaches to taking body measurements, while manufacturers decide their own finished-garment specifications.
Frequently asked questions
Which method should I use?
Start with the classic method if you commonly buy traditional US or UK sizing. Try the direct method when a brand recommends a band close to your measured underbust. Compare both with the brand chart and assess real fit.
Why does the cup letter change with band size?
Cup letters describe volume relative to the band, not one fixed volume. A 34C is not the same cup volume as a 38C.
Should I measure with a bra on?
A non-padded bra can help support the bust during measurement. Avoid heavy padding or compression because it can change the full-bust measurement.
Can two sizes both fit?
Yes. Sister sizing, body shape, and different bra designs mean neighboring sizes may both be comfortable.