Bra size calculator
Enter your measurements once and see your size converted across six sizing systems used around the world.
Measure the band snugly around your ribcage, directly under the bust, and the bust around the fullest point — both while wearing a well-fitting (or no) bra, tape parallel to the floor.
Fill in the fields and press Calculate to see your result here.
How this calculation works
The band size uses the common “measure and round, then add 4 or 5” method: your underbust measurement is rounded to the nearest whole inch, and 4 is added if that number is even or 5 if it's odd, giving a standard even band size. The cup size comes from the difference between your bust and underbust measurements — each inch of difference steps up one cup letter. Sizing systems then relabel the same physical size differently: EU and Germany/Italy/Netherlands use a plain cm-based band with a straightforward A–J letter scale, France/Belgium/Spain use the same cm band but shift the cup letter up by one, and UK/Australia and the US diverge slightly in cup lettering above a D cup. Because these are general published conversion norms rather than a single global standard, and because cut and fit vary a lot between brands, treat the result as a helpful starting point rather than an exact fit — always try a bra on where possible.
Sizing note: Results are a general starting point. Sizing systems and fit vary by country and brand, so try garments on when you can.
Tips
Measure over a well-fitting bra or bare skin
A loose or padded bra under the tape measure throws off both numbers — measure directly against your body or a thin, unpadded bra for the most accurate starting point.
Brands vary more than sizing systems do
Two brands in the same country can fit a labelled size very differently — use this as a starting point for which size to try on, not a guarantee of fit.
Try sister sizes
If the band feels loose or tight, sister sizes (one band size up with one cup size down, or the reverse) hold roughly the same cup volume.
Sizes change over time
Weight changes, life stages and different styles can all change your best size. Re-measure every so often.
Use it as a starting point
Sizing systems and cup progressions differ by country and brand, so try on a few options before deciding.
Frequently asked questions
Why do France/Belgium/Spain show a different letter than Germany or the EU standard?
It's a long-standing regional convention: for the same physical cup volume, French-system sizing labels it one letter higher than the wider EU/German scale. A German ‘C’ and a French ‘D’ can describe the same actual size.
Why does the US differ from the UK above a D cup?
The two countries' cup-letter sequences diverge once you pass D: the US commonly uses DD and DDD, while the UK continues with DD, E, F and so on for the same sequence of sizes.
Is this exact for every brand?
No — it follows commonly published general conversion charts, but cut, fabric and brand sizing philosophy all cause real variation. Use it as a starting point, not a guarantee.