What is a cup size?
A cup size is the volume part of a bra size — shown as a letter (A, B, C, D, DD…) and always paired with a band number, like the "C" in 34C. It's set by the difference between your bust (fullest part) and your band (snug underbust): each inch of difference is one cup. A 1-inch difference is an A, 2 inches a B, 3 inches a C, 4 inches a D, and up from there. Because the letter is relative to the band, the same letter is a different volume on a different band — a 32C is smaller than a 36C.
In plain terms: the letter is how much fuller your bust is than your ribcage. Need your full size, a calculator, and sister sizes? See the complete bra sizes guide.
One quick distinction first: this guide is about the cup — the letter. For your complete bra size, the full measuring method, a size calculator, and sister sizes, head to the bra sizes guide. For what determines your size and how it changes over life, see breast sizes.
- Cup = the letter (A, B, C, D, DD…); band = the number. Together they make your size.
- Each inch of bust-minus-band difference = one cup: 1″=A, 2″=B, 3″=C, 4″=D, 5″=DD/E.
- Order (US): AAA, AA, A, B, C, D, DD (E), DDD (F), G, H, I, J…
- DD ≈ E and DDD ≈ F — US stacks D's where UK uses single letters.
- The same letter ≠ the same volume: a 32C is smaller than a 36C.
- Cup too big? Gaps & wrinkling. Too small? Spillage & falling out when you bend.
- Sizing varies by brand — always check the brand's chart and try styles on.
What Is a Cup Size?
A bra size has two parts: a band (the number, like 34) that wraps your ribcage and provides most of the support, and a cup (the letter, like C) that holds the breast. The cup size isn't an absolute volume — it's the difference between your bust and your band. Measure around the fullest part of your bust, measure snugly under your bust for the band, and subtract: every inch of difference is one cup size.
That's the single most important idea on this page: the cup letter is relative to the band. A 32C, a 34C, and a 36C all say "C," but each holds more than the last, because the band underneath it is bigger. So "what does a C look like?" has no single answer until you know the band it's sitting on — which is exactly why two people can both wear a C and look completely different.
Cup Sizes in Order (Smallest to Largest)
In US sizing, cup sizes run from smallest to largest like this:
AAA › AA › A › B › C › D › DD (E) › DDD (F) › G › H › I › J …
Two things worth knowing about that sequence:
- US "stacks" the D's. Above D, US sizing usually writes DD and DDD rather than E and F — so DD ≈ E and DDD ≈ F. That's also why people ask "why is there no E cup?" — there is; it's just labeled DD.
- UK and EU differ past D. UK sizing runs D, DD, E, F, FF, G… as single letters, so a US DD and a UK E can mean the same cup. Once you're past D, always check whether a chart is US or UK.
And remember: this is the cup order on a single band. Real sizes are a grid — band and cup together — which is why a 30G and a 38D can hold a similar volume on very different frames. That's the sister-size idea, covered fully in the bra sizes guide.
Cup Size Chart
Here's the core cup chart: the difference between your bust and band, and the cup it corresponds to. (US labels, with the UK single-letter equivalent past D.)
| Bust − Band difference | US cup | UK cup |
|---|---|---|
| Less than 1 inch | AA (or AAA) | AA |
| 1 inch | A | A |
| 2 inches | B | B |
| 3 inches | C | C |
| 4 inches | D | D |
| 5 inches | DD | DD / E |
| 6 inches | DDD | E / F |
| 7 inches | DDDD / G | F / FF |
| 8 inches | H | FF / G |
| 9 inches | I | GG |
| 10 inches | J | H / HH |
Past D the US and UK labels drift apart, and brands aren't perfectly consistent — so treat the larger end as a guide and always confirm with the specific brand's chart. For everyday US sizes (A–DD), the chart above is reliable.
How to Find Your Cup Size
Two measurements give you your cup. Use a soft tape, wear an unpadded bra (or none), and keep the tape level with the floor.
- Band (underbust): wrap the tape snugly around your ribcage directly under your bust. Round to the nearest even number — this is the modern method; don't add inches the way older guides told you to.
- Bust (fullest): measure around the fullest part of your breasts, tape level and not pulled tight.
- Subtract: bust minus band. Each inch of difference is one cup — 1″ = A, 2″ = B, 3″ = C, 4″ = D, and up. Match it to the chart above.
Worked example: if your underbust is 33″, your band rounds to 34. If your bust is 38″, the difference is 4″ — a D cup. So your starting size is 34D. Try it yourself below.
Find Your Cup Size
Enter your two measurements — we'll do the math and give you a starting cup and size.
A starting point, not a verdict — fit varies by brand and style. For your full size, sister sizes, and the complete method, see the bra sizes guide.
What Each Cup Size Means
A quick, body-positive tour of the everyday range. Remember these describe the bust-to-band difference, not how you "should" look — every cup is normal and beautiful, and the band it's on changes everything.
A & B Cups
A gentle to moderate difference between bust and band. A and B cups suit lighter, less structured styles beautifully — bralettes, soft cups, and demi shapes feel great and look natural, and front-fastening or wireless bras are very comfortable here. If you'd like more shape, a lightly padded or push-up style adds it easily.
C & D Cups
The most common everyday range, and the point where genuine cup containment starts to matter. C and D cups do well in molded/contour t-shirt bras, balconettes, and plunges, and a supportive underwire or sectioned cup keeps everything lifted and smooth. This is the range most brands build the widest selection around.
DD, DDD & Beyond
A fuller cup that benefits most from real support: a firm band (it carries the weight), sectioned full-coverage cups, wider padded straps, and several hook columns. Fit precision matters more here, and sister sizing becomes a useful tool when a band feels off. Specialist full-figure ranges go well past DDD into G, H and up.
Why the Same Cup Fits Differently
Two reasons your "C" might not be someone else's "C" — or even your own across brands:
1. The cup is relative to the band. Because the letter is a difference, a 32C, 34C and 36C grow in actual volume as the band grows. This is the basis of sister sizes: if your band feels too tight but the cup is right, going one band down and one cup up (or the reverse) keeps the same cup volume on a better-fitting band. The bra sizes guide walks through sister sizing in full.
2. Brands aren't consistent. Cup sizing varies between brands and countries — a C in one label can fit like a B or D in another, especially past D where US and UK diverge. That's not you doing anything wrong; it's the industry. The practical takeaways: always check the specific brand's size chart, and treat your calculated size as a starting point to try on, not a fixed rule.
A few signs your cup isn't right: too small shows as spillage, the cup cutting in, or breasts escaping when you bend over; too big shows as gaps, wrinkling, or cup fabric that folds instead of filling. In both cases, adjust the cup (and double-check the band, since a loose band often masquerades as a cup problem).
Cup Sizes FAQ
Which cup size is bigger: A, B, or C?
Which cup size is bigger: A or D?
What are the cup sizes in order from smallest to largest?
Is a DDD the same as an F?
Why is there no E cup size in US sizing?
What is the smallest cup size?
What is the biggest or largest cup size?
How do I find my cup size?
How do I know if my bra cup is too big?
Why do my breasts fall out of my bra when I bend over?
What is the average cup size, and is a C cup average?
Does the same cup letter mean the same size on every band?
What size is 34DDD equivalent to?
Is a D cup big, and is it the smallest?
This guide is educational and body-positive — every cup size is normal, and the "right" size is the one that fits and feels good. Cup sizing varies by brand and country, so treat measurements and charts as starting points and try styles on. The calculator gives an estimate, not a fitting. Last reviewed: May 20, 2026.
