Bra Cup Sizes Explained: AA to K Chart, Sizes in Order and How to Find Yours

Understanding Bra Cup Sizes: A Historical Perspective

Supportive undergarments exist in some form across most of recorded history, from bands of linen to boned corsets. The modern bra, with two separate cups and a band that carries the weight, took shape in the early twentieth century. For its first decades it was sold in a handful of general sizes, with little attention to the difference between a narrow ribcage and a full bust.

That changed in the 1930s. S.H. Camp and Company is generally credited with introducing lettered cup sizes in the early 1930s, and Warner's brought A, B, C and D cups into mainstream retail a few years later. The idea was simple and lasting: describe the bust separately from the ribcage, so the same band could be sold with cups of different depth.

What did not last was agreement on what came after D. As larger cups became widely available later in the century, American brands extended the D by repeating it, to DD and then DDD. British brands introduced new letters instead, moving from DD to E, F and FF. European brands used single letters throughout and never adopted DD at all. Those three decisions are the root of almost every cup size mix-up shoppers run into today, and they are covered in detail in the sizing systems section below.

How Are Bra Cup Sizes Determined?

A bra size has two parts. The band is the number, like 34, and it wraps your ribcage and carries most of the support. The cup is the letter, like C, and it holds the breast. The cup letter is not an absolute volume. It is the difference between your bust measurement, taken around the fullest part of the breasts, and your band measurement, taken snugly just beneath them.

The larger that difference, the larger the cup letter. Each inch is one step: a 1-inch difference is an A, 2 inches a B, 3 inches a C and 4 inches a D. From there the US sequence continues DD at 5 inches and DDD at 6.

Cup size is not static; it moves with the band. A 32D and a 36D share a letter, but the 36D holds noticeably more volume because each inch of difference is measured around a larger ribcage. This is the single most important idea in cup sizing, and it explains why a D on one person can look modest while a D on another looks full.

Bra Cup Sizes in Order, Smallest to Largest

In US sizing, cups run from smallest to largest in this order:

In UK sizing, the same cups run in this order:

Three things are worth knowing about those sequences:

• They agree through DD. A US DD and a UK DD are the same 5-inch cup. The labels only split after that.
• The US repeats the D, then jumps. After DD comes DDD, and after DDD most US brands go straight to G rather than writing DDDD. So a US G is the 7-inch cup, the same as a UK F. Our DDD guide covers the step in detail.
• The UK doubles some letters. After F come FF, then G, then GG. Those doubled letters are half-steps in name only; each is one full inch of difference, like every other cup.

Smaller than A there is AA, and some brands make AAA. At the top, there is no fixed maximum: full-bust specialists produce cups well past K. And remember that this is the order on a single band. Real bra sizes are a grid of band and cup together, which is why a 30G and a 38D can hold a similar volume on very different frames.

Bra Cup Size Chart

Through D, every system agrees. From 5 inches on, read the column for the system the brand uses. If you are unsure which that is, look at what follows DD on the brand's own chart: DDD means US labels, E means UK labels. For band conversions across countries, see the bra size conversion chart.

Different Bra Sizing Systems: US, UK, EU and Beyond

Three sizing systems cover most of the bras sold in the US: American, British and European. A shopper buying from brands based in different countries meets all three, sometimes on the same website. The differences fall into two groups: how the band is numbered and how the cup is lettered.

Bands. The US and UK number bands in inches: 32, 34, 36. European sizing numbers bands in centimeters, so a US 34 is an EU 75. French and Spanish sizing add 15 to the European number, so the same band is a 90. Australian sizing subtracts 22 from the inch band, so a 34 becomes a 12. Italian sizing counts bands from 1.

Cups. This is where the confusion lives. The US and UK agree through DD, then split. European sizing never used DD, so it runs one letter ahead of the UK from 5 inches on: a UK DD is an EU E, and a UK E is an EU F.

A practical consequence: many full-bust brands sold in the US use UK labels. A shopper who knows she wears 36DDD and filters a site for DDD will miss every 36E on the shelf, even though those bras are cut for exactly her size. Searching both labels roughly doubles the range available above DD.

How to read a brand size chart in four checks

1. Find the step after DD. If the next cup is DDD, the brand uses US labels. If it is E, the brand uses UK labels. If there is no DD at all and the chart runs D, E, F, it is using European letters.
2. Check the band units. Bands of 30, 32 and 34 are inches. Bands of 65, 70 and 75 are centimeters, European style. Bands of 80, 85 and 90 are usually French or Spanish. Convert before comparing.
3. Look for doubled letters above F. FF, GG and HH are UK half-steps in name only. Each is one more inch of difference, so a UK FF is a US H, not something between F and G in volume.
4. Read the fit notes. Many brands say whether a style runs small in the band or shallow in the cup. A note like "size up in the band" usually means the sister size, not a larger cup letter.

Those four checks take a minute and prevent most returns caused by labeling rather than fit. When a brand publishes its own measurement table in inches or centimeters, match your two measurements to it directly rather than converting your letter. The table reflects how the garment was actually cut, and it removes the guesswork about which letter convention sits behind the label. For brands sold in several countries, the same style can carry a US label on one site and a UK label on another, so check the chart on the site you are buying from.

Certain brands also use their own conventions, sizing in S, M and L, or combining sizes such as C/D. For those, the brand's own chart is the only reliable guide. For every band and cup across all systems, the bra size conversion chart is the full reference.

How to Find Your Cup Size

Two measurements give you your cup. Use a soft tape, wear an unpadded bra or none at all, and keep the tape level with the floor.

Left: measure snugly under the bust for your band. Right: measure around the fullest part for your bust.

1. Measure your band. Wrap the tape snugly around your ribcage directly under the bust, level all the way around, at the end of a normal breath out. Round to the nearest even number. Add nothing to it.
2. Measure your bust. Measure around the fullest part of your breasts, tape parallel to the floor, resting rather than pulled tight.
3. Subtract. Bust minus band. Each inch of difference is one cup: 1 inch A, 2 B, 3 C, 4 D, 5 DD, 6 DDD, 7 G. Match it to the chart above, or let the calculator below do it.

The calculator gives an estimate, not a fitting. For the complete method, including how to judge the band on the body and when to use a sister size, see the full bra sizes guide or the bra size calculator.

Finding the Perfect Fit: Tips for Measuring and Fitting

What Each Cup Size Means

Which Bra Styles Suit Which Cup Sizes

As cup size grows, the job a bra has to do changes. At the small end the main goals are shape and comfort, and light construction is enough. In the middle, the cup has to contain and lift, and molded or seamed cups with a supportive wire earn their place. At the full end, the band carries real weight, the cup has to hold its shape under movement, and construction details such as side panels, deep bands and multiple hook rows stop being optional.

Two patterns stand out. Light, unstructured styles work best at the small end, where there is little weight to carry. Seamed, full and side-support cups work best at the full end, where a single molded piece cannot direct the tissue. The middle range, C to D, has the most freedom, which is why brands build their widest selection there.

Cup Size Is Not Breast Shape

Two people with the same cup size can need very different bras, because cup size describes volume, not shape. A cup letter says how much fuller your bust is than your ribcage. It says nothing about whether that volume sits high or low, close together or wide apart, projected forward or spread across the chest.

Shape is often the reason a correctly sized bra still feels wrong. A bottom-full bust tends to leave an empty upper cup in a full-coverage style and fills a balconette well. A top-full bust may spill over a balconette and suits a full cup or a stretch-lace upper edge. A wide-set bust sits toward the underarm and benefits from side support. A projected bust needs a deep cup rather than a wide one. A shallow bust spreads across the chest and often suits a wider, shallower cup such as a demi or balconette.

If your measured cup is right but the fit still is not, change the style before changing the size. Our breast shapes guide matches each shape to the constructions that suit it.

Breast Cup Size Comparison: Why the Same Letter Differs

Because the cup letter is a difference, cup volume grows with the band. A 32C, 34C and 36C step up in real volume even though each is a C. Move one band down and one cup up, and the volume stays roughly the same: those equal-volume sizes are called sister sizes. The table shows how cup volume lines up across bands.

Read across a row and every size holds a similar cup volume. Read down a column and volume grows with each letter. This is why "what does a C cup look like?" has no single answer, and why a comparison photo of cup letters without band sizes tells you very little. Our sister sizes guide covers the full grid, and the D vs DD vs DDD comparison works through the most searched step.

Size F: UK F or US F?

Searches for "size F" mean different things depending on the label. A UK F is a 7-inch difference, the same cup as a US G. An EU F is a 6-inch difference, the same cup as a US DDD and a UK E. A handful of US brands also use F for their 6-inch cup. Before assuming an F is larger or smaller than your DDD, check which system the brand uses. The F cup guide walks through each case, and F cup bras are stocked under both conventions.

Is my cup size big, small or average?

Studies commonly place the average US bra size somewhere around 34C to 34DD, but averages shift over time and differ between studies. What matters for fit is not where a letter ranks but whether the bra fits the band and cup you actually measure. Our average bra size guide covers the numbers and their limits.

Signs Your Cup Size Is Wrong, and What to Try

A loose band often disguises itself as a cup problem. Check the band first: if it rides up, the whole bra tilts, the cups sit wrong, and changing the cup alone will not fix it.

Common Misconceptions About Bra Cup Sizes

The letter on a bra is a measurement, not a verdict. Once you know it describes a difference, every other rule about cup sizes makes sense.

HauteFlair Fit Team

Shop Bras by Cup Size

Frequently Asked Questions About Bra Cup Sizes

Conclusion

A bra cup size is a single measurement: the difference between your bust and your band. Each inch is one letter, and the letter always depends on the band it sits on. That one idea explains why a 32D and a 36D differ, why sister sizes work, and why a cup letter on its own tells you so little.

The rest is labeling. The US, UK and EU agree through DD, then split: US DDD, UK E and EU F are the same cup, and a US G matches a UK F. Knowing which system a brand uses, and searching both labels above DD, opens up far more of the bras that fit.

Measure carefully, round the band to the nearest even number, and treat the result as a starting size to try on. A good fit is one where the band sits level, the gore lies flat, and the cup holds everything without gaping or spilling. From there, the style you choose is up to you.

This guide covers bra sizing conventions and garment fit and is for informational purposes only. Cup labeling varies between manufacturers and countries, and a minority of charts differ from the convention used here; the brand's own size chart is the most reliable guide for any specific garment. Home measurements and calculator results are a starting point rather than a guarantee. Any new or unexplained change in breast size, shape, skin or sensation should be discussed with a doctor. Last reviewed September 2026.