Your cup size is the difference between your bust measurement and your band measurement, measured in centimeters. Every 2 centimeter difference stands for exactly one cup size: 12 to 14 cm is an A, 14 to 16 cm a B, and so on up to a J at 30 to 32 cm. In the cup size chart below you can see straight away which letter matches your difference. And just as important: why that same letter can mean a completely different bra at a different band size.
Cup size chart: from AA to J in centimeters
Subtract your band measurement from your bust measurement. The number of centimeters left over is your cup size. Look up that difference in this cup size chart and you'll know which letter you have.
| Difference bust and band | Cup size (EU) | Good to know |
|---|---|---|
| 10 to 12 cm | AA | The smallest standard cup |
| 12 to 14 cm | A | Same in EU, UK and US |
| 14 to 16 cm | B | Same in EU, UK and US |
| 16 to 18 cm | C | Same in EU, UK and US |
| 18 to 20 cm | D | Up to here the systems match |
| 20 to 22 cm | E | Called Double-D (DD) in the US system |
| 22 to 24 cm | F | Above D the systems start to differ |
| 24 to 26 cm | G | Support now matters more than the letter |
| 26 to 28 cm | H | Larger cup: choose based on fit with the Luma Forma |
| 28 to 30 cm | I | Larger cup: view plus size bras |
| 30 to 32 cm | J | The largest standard cup; if in doubt, check size advice |
The step between two letters is always 2 centimeters. If you fall exactly on a border, for example at 18 cm, round up to the larger cup (here a D) and then assess how the fit feels. Half a centimeter of measuring difference can push you a letter higher or lower, so take your time and measure twice.
How do you calculate your cup size? Two measurements
For a reliable cup size you need two numbers: your band measurement and your bust measurement. Measure both with an ordinary tape measure, straight and horizontal around your body. Do it in front of a mirror, so you can see if the tape isn't sagging at the back.
1. Measure your band size
Place the tape measure snugly, directly under your bust, exactly where your bra band sits. Breathe out calmly and read off the number. This number determines your band size, the number before the cup letter.
| Underbust measurement | Band size (EU) |
|---|---|
| 63 to 67 cm | 65 |
| 68 to 72 cm | 70 |
| 73 to 77 cm | 75 |
| 78 to 82 cm | 80 |
| 83 to 87 cm | 85 |
| 88 to 92 cm | 90 |
| 93 to 97 cm | 95 |
2. Measure your bust
Now measure around the fullest part of your bust, usually at nipple height. Keep the tape loosely in place here, so it doesn't press into your skin anywhere. Then subtract your underbust measurement from this number and look up the difference in the cup size table above.
Tip: measure without a padded or push-up bra, and preferably at a calm moment during the day, not right after exercising or a large meal. A centimetre too tight or too loose can easily make half a cup size difference, and you'll notice that later in the fit.
Why the same cup size feels different every time
A cup letter says nothing about volume on its own. It only describes the difference relative to your band size. A D at band size 70 has a noticeably smaller cup than a D at band size 90, even though the label shows the same letter. The cup grows along with every band size you go up.
That's why shopping by letter alone doesn't work. The band carries most of the weight and determines how the cup sits in place. If your band fits well and stays neatly horizontal on your back, you've got the foundation right. Our guide to measuring your bra size shows step by step how these two work together.
Sister sizes: same cup, different band size
Because the cup moves along with the band size, every size has a few so-called sister sizes: sizes with exactly the same cup volume, but a different band. Go up a band size, and you go down a cup letter to keep the same volume. And the other way around: a smaller band size means a larger cup letter.
An example: 70E, 75D, 80C, 85B and 90A all have the same cup volume. If your band pinches but the cup fits well, you move up to the next sister size with a roomier band and one letter up. In our guide to sister sizes you can work this out for your own size.
Larger cup sizes (E to J): what matters most
From an E cup upward, the construction of your bra matters more than the letter on the label. More volume calls for a wide, sturdy band, high side panels that prevent bulging, and cups that shape without cutting into your skin. An underwire isn't the only way to achieve this; good support is possible without one too.
The Luma Forma Bra 2.0 (€43.15) is built on that foundation: integrated memory foam cups for support without underwire, Side-Boning Technology 2.0 in the side panels that prevents spillage, and a double-layered, invisible design. It comes in 13 sizes, including plus in-between sizes like S+, M+ and L+, so larger cups don't get stuck with a single standard size. You'll find more options in the plus size bra collection.
From cup size to S, M or L: how to read a seamless bra
Many seamless bras don't work with separate band and cup sizes, but with standard sizes like S, M and L. That's not a sales trick: thanks to the stretchy, seamless fabric, a single size covers a small range of band and cup sizes. Useful, as long as you know where you fall within that range.
So first work out your band size and cup size using the charts above. Compare them to the product's size chart, or use our size advice to check. If you fall at the upper end of a cup range, check whether a style with in-between sizes, such as the Luma Forma, comes closer to your size than a regular S, M or L.
International cup sizes: EU, UK and US
Up to and including the D-cup, Europe, the United Kingdom and the United States use the same letters. Above that, the systems diverge. An EU E is called a DD (Double-D) in the US system, and the UK system stacks letters with DD, FF and GG. A German 75F is therefore not automatically a British 75F.
If you shop at a foreign retailer, always go by their own size chart rather than just the letter you're used to. The centimetres from our cup size chart remain your fixed anchor point, because a difference of 20 cm stays 20 cm, no matter which country you're shopping in.
Frequently asked questions about cup sizes
What does the letter in my cup size mean?
The letter represents the difference between your bust measurement and your band measurement. Every 2 centimetre difference is one letter higher: 14 to 16 cm is a B, 16 to 18 cm a C, and so on. So the letter says something about that difference, not about your bust size on its own, separate from your band size.
Is a DD the same as an E?
In the European system, an E-cup is equal to a US Double-D (DD). The confusion arises because the American system inserts a double letter after the D, while Europe simply continues on to E. If you calculate using centimetres, you always arrive at the same difference.
How many centimetres are there between two cup sizes?
Standard is 2 centimeters. The difference between your bust and underbust measurement determines, in steps of 2 cm, which cup you take. If you fall on a border, round up and check the fit before settling on a size.
Can I keep the same cup and still buy a different size?
Yes, through your sister sizes. If you go up one band size and down one cup letter, or the other way around, you keep the same cup volume. This way you adjust the band to your body without the cup becoming too small or too large.
Which cup size is the largest?
Common size charts go up to an H, I or J, and sometimes a K. In this cup size chart it stops at J, meaning a 30 to 32 cm difference. With larger cups, focus mainly on the band and construction, not just the letter.
Why doesn't my cup size online match the shop?
Brands and countries use slightly different size charts, and fabrics stretch differently. That's why you might be a C with one brand and a D with another. Measure yourself in centimeters and check each brand's own size chart before ordering.
How do I know my size without a tape measure?
Take a bra that fits you well and whose band doesn't ride up your back. Its size label is your best starting point. If you're not sure, use our size advice to check your size.
How to translate the chart into your size
Measure your underbust and your bust, subtract them from each other, and compare the difference to the cup size chart. Your band size and your cup letter together form your size. If you're unsure between two cups, choose based on fit: our size advice can help you further, and the Luma Forma with half sizes takes care of just that bit of doubt for you.
Written by Team Novyre, specialists in seamless underwear. Last updated: 7 August 2026.
