Free Online Calculators
Underbust + bust → bra size EU and US with measuring guide
Enter your underbust and bust measurements in centimetres to instantly find your bra size in EU, UK and US formats. The band is your underbust rounded to the nearest 5 cm, and the cup letter comes from the difference between bust and band, one letter per 2 cm. Use our measuring guide to make sure you get accurate results.
Tip: Measure snugly, horizontally, without a bra.
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Adding four inches goes back to an old fitting method from the era of stiff, non-stretch bra fabrics, which needed extra length to be comfortable. Modern bras use elastic bands, so most fitters now measure your underbust snugly and use that number directly.
A bust measurement on its own doesn't give you a cup size, because the cup comes from the difference between your bust and your underbust. The same bust can be a smaller cup on a wide ribcage and a larger cup on a narrow one.
"A handful" isn't a bra size — hand sizes vary and cups only make sense in relation to a band measurement. The same breast volume gets a different cup letter depending on the band it sits on.
Yes, you only need a soft tape measure and a mirror. Measure your underbust snugly and your bust at the fullest point while standing straight, then compare the two numbers to get band and cup.
Measure snugly around your ribcage directly under the bust for the band, then loosely around the fullest part of the bust. The difference between the two measurements determines the cup letter, while the underbust measurement determines the band number.
They are sister sizes, so the cup volume is roughly the same, but the band is not — the 36 band is looser. If a bra feels right in the cup but too tight around, going up a band and down a cup letter keeps the volume similar.
It will fit tighter around your ribcage and the cups will feel smaller, because dropping the band without changing the letter reduces cup volume. If you need the smaller band, the sister size with the next cup letter up keeps the volume the same.
There is no prettiest size — a bra size is just a measurement, not a rating. What actually shows is fit: a band that sits level and cups that fully contain the breast without gaps or spillage.
Appearance varies a lot between people with the same size, since shape, breast tissue distribution and torso proportions all differ. A cup letter only describes the difference between bust and underbust, not projection, fullness or position.
Getting the right bra size makes an enormous difference in comfort, posture, and confidence. Yet studies suggest that up to 80% of women are wearing the wrong bra size without even knowing it. Our free Bra Size Calculator takes the guesswork out of bra shopping by converting your underbust and bust measurements into EU, UK and US bra sizes instantly.
Accurate measurements are the foundation of a perfect fit. Before you use the calculator, grab a soft measuring tape and follow these steps carefully.
Wrap the measuring tape firmly around your torso, directly underneath your breasts. The tape should sit snug against your skin but not dig in. Keep it parallel to the floor all the way around. Breathe out normally and note the measurement in centimetres. The calculator takes centimetres, so multiply inches by 2.54.
Now wrap the measuring tape loosely around the fullest part of your chest, usually across the nipple line. Make sure the tape stays level across your back and does not pull or sag. Note this measurement as well.
Enter both figures in centimetres into the Bra Size Calculator above and hit Calculate. Your EU, UK and US bra sizes appear instantly, together with the difference between your bust and the band.
Bra sizing systems vary across the world, which can make international shopping confusing. Here is a quick breakdown of the two most common systems.
In the United States, band sizes are expressed as even numbers (32, 34, 36, 38, and so on) and cup sizes run from AA through DDD and beyond. A US size 34B, for example, means a 34-inch band with a B cup.
European sizing uses centimeter-based band measurements (65, 70, 75, 80, and so on) paired with cup letters. The cup progression in the EU system is slightly different from US sizing, so a direct conversion is always helpful when buying from European brands.
UK bands are the same as US bands. Cup letters A to D are the same in all three systems; after that they diverge: EU E = UK DD = US DD, EU F = UK E = US DDD, EU G = UK F = US G, EU H = UK FF = US H.
The math behind bra sizing is straightforward once you know the formula.
For example, if your underbust is 76 cm and your bust is 89 cm, the band rounds to 75 EU / 34 UK and US and the difference to the band is 14 cm, which corresponds to a B cup — giving you a final size of 75B (EU), 34B (UK) and 34B (US).
Even with the right size on paper, fit can vary between brands and styles. Keep these practical tips in mind when trying on bras.
Your bra size is not fixed for life. It is worth recalculating whenever you experience significant body changes, including:
Experts recommend measuring yourself at least once a year and before any major bra shopping trip.
Sizing is not fully standardized across the industry. Different brands use slightly different grading systems, fabrics, and construction methods. Always try bras on when possible, or consult the brand-specific size chart and use our calculator result as a reliable starting point.
If your underbust measurement sits between two standard band sizes, try both and see which feels more comfortable. Many people also use sister sizing — for example, if a 34B feels tight in the band but the cup fits well, try a 32C, which has a smaller band but an equivalent cup volume.
Our Bra Size Calculator uses universally accepted measurement formulas and works for all body types. That said, body shape, breast position, and personal comfort preferences can influence the ideal style or cut of bra, even when the size calculation is correct.
Yes, but convert first: the calculator takes centimetres only. Multiply inches by 2.54, so a 30-inch underbust is 76.2 cm and a 35-inch bust is 88.9 cm, which gives 75B (EU) and 34B (UK and US).
Sister sizing refers to adjacent bra sizes that share the same cup volume but have different band sizes. For instance, 34B, 36A, and 32C are all sister sizes because the cup capacity is equivalent. Going up a band size means going down a cup letter, and vice versa. This is a useful trick when a perfect fit in one dimension leaves the other slightly off.