Breast Sizes: Cup Size Chart AA–H & Breast Size Calculator

The Complete Breast Size Chart (Cup Sizes by Measurement)

This is the core reference. Find your bust-to-band difference in the first column and read across for your cup size in each system. The letters are identical through DD, then the US, UK, and EU systems diverge, so above a D cup always confirm which system a label uses. The final column links straight to that cup in our range.

A complete bra size pairs this cup letter with your band number, which is your underbust rounded to the nearest even inch. So a 4-inch difference on a 34 band is a 34D; a 6-inch difference on the same band is a 34DDD in the US or 34E in the UK.

Every Cup Size, Explained

The chart gives you the letter. This section gives you what the letter actually means: the measurement behind it, how it is labelled elsewhere, what tends to fit well at that size, and where to find it. Cup sizes are listed by US label, with UK and EU equivalents noted where they diverge.

How Breast Volume Changes Across Cup Sizes

Each cup letter adds roughly the same step of volume at a given band, and each band size up adds about 20% more volume at the same letter. The visual below shows the progression from a petite bust through to a fuller bust; the chart above gives the exact cup each step corresponds to.

Because the figures above are tied to one band, they isolate what the letter actually adds. Here is the same data as a quick reference, approximate volume per cup at a 34 band, in milliliters (1 mL = 1 cc):

Move up one band at the same letter and each figure rises by roughly 20%, which is why a 30D and a 38D hold visibly different volumes despite sharing the letter. Control for the band, and the cup letter finally means something consistent.

Cup Size Calculator

Enter two measurements and the calculator returns your cup size, in US, UK, and EU labels, plus your full bra size. It is the chart above, done for you. Switch between inches and centimeters as needed.

How to Measure for the Chart

The chart only works with two accurate numbers. Here is the quick version; for the full method, band-fit checks, and sister sizing, see our complete how to measure your bra size guide.

Six Measuring Mistakes That Change Your Result

Most people who get an implausible result from a calculator have made one of these, and each one shifts the answer by a full size or more.

Breast Size and Breast Shape Are Different Things

This is the part a size chart cannot tell you, and it explains the most frustrating experience in bra shopping: measuring carefully, buying the right size, and finding it still does not fit.

Size is volume. It is the cup letter, and the chart above gives it to you. Shape is how that volume is arranged on your chest, and it is described by three independent properties.

None of these three appears on a size chart, and none of them changes your cup letter. They change which bra in that letter will fit you, which is why two people who both measure 34DD can need completely different styles.

Sister Sizes: the Same Cup on a Different Band

Cup volume is a ratio, which has a useful consequence: you can change the band and keep the volume, as long as you move the cup letter the opposite way.

Go down one band and up one cup and the volume stays the same. Go up one band and down one cup and the same applies. These are sister sizes, and 34C, 32D and 36B all hold roughly the same cup volume on different frames.

Sister sizing is genuinely useful in three situations: when your measured size is out of stock, when a particular brand's band runs tight or loose, and when the band is riding up but the cup fits, which calls for a tighter band and a larger cup rather than a smaller size overall. Our full sister size guide covers the mechanics in detail.

Why the Same Cup Size Fits Differently in Different Brands

You measure a 34DD, buy a 34DD, and it fits perfectly. You buy a different brand's 34DD and it is unwearable. Nothing has gone wrong with your measuring.

Bra sizing is not standardised. No regulatory body enforces consistency between manufacturers. The measurements behind a size are fixed, but each brand decides how much volume to allocate at that label and, more importantly, what shape to build it in.

Every brand drafts its patterns around a house shape: a particular wire curvature and width, a cup depth relative to width, a point where the straps attach, a band firmness, a gore height. That shape repeats across the whole range, which is why people who find a brand that works stay with it for years and why the identical size elsewhere can feel completely wrong.

Two practical consequences. First, your size is a starting point rather than a guarantee, and the brand's own chart is more reliable than a general one. Second, if a size fails in one brand, test a different construction rather than a different size: a seamed cup, a moulded cup and a stretch-edge cup tell you far more than three styles from the same house. Our guide to bra brands by house shape covers how each one runs.

Cup Size Chart: US, UK & EU Conversions

Cup labels are identical through DD, then the systems part ways. This is the conversion to bookmark if you shop international brands, and note that EU sizing uses single letters throughout, so it runs one letter ahead of the UK from DD upward.

The band number converts too: a US/UK 34 band is an EU 75 and a French 90. For the full multi-country reference across every band and cup, see our bra size conversion chart, and for why the letters diverge in the first place, our UK vs US sizing guide.

Why Your Cup Size Changes Over Time

A size that fitted perfectly two years ago may not now, and that is normal rather than a sign you measured wrong the first time. Breast volume responds to several things, and the ribcage changes too.

The practical rule: re-measure every six to twelve months, and after any noticeable body change. If a long-held size suddenly fits differently, measure both band and cup before assuming the bra has worn out, because often both have changed.

One nuance worth knowing for cycle-related change: a cup with a stretch lace or power mesh upper edge accommodates week-to-week variation far better than a rigid moulded cup, which is usually a better answer than owning two sizes. Pregnancy and nursing are a separate case, where fit changes fast enough that purpose-built nursing bras with stretch cups make more sense than repeatedly re-buying.

Five Breast Size Myths Worth Correcting

Average and Most-Common Breast Size

The average US bra size is frequently cited as around a 34DD today, up from a 34B a few decades ago. Most of that shift reflects better fitting and wider size ranges rather than bodies changing, and "average" is not the same as "common." Sizes spread widely across the population, C and D cups are the most frequently worn, and a large share of people wear the wrong size entirely.

It is also worth being precise about what an average cup letter means, which is: very little. Because the letter is a ratio, an average of 34DD tells you about the pairing rather than about volume. A population with a smaller average band would report a larger average cup at identical volumes.

The practical takeaway: population averages make poor sizing advice. Your measured size, from the chart and calculator above, is the only number that fits you.

"A cup letter is a ratio, not a measurement. The most useful thing a breast size chart does isn't telling you what's average. It's turning two numbers you can measure at home into a size you can actually shop. Read the letter, anchor it to your band, and the rest follows."

— HauteFlair Fit Editorial Team

Which Bra Styles Suit Which Cup Sizes

Style advice that ignores cup size is the reason so much of it is useless. Construction requirements change as volume increases, so a recommendation that is entirely sensible at a B cup can be unhelpful at a G.

Two style notes that cut across the whole range. Wireless works at any size when it is built with a firm band and seamed cups, and fails at larger sizes when it is not, which is a construction issue rather than a size limit. And strapless depends entirely on band firmness, since with no straps the band does one hundred percent of the work, which is why it is harder above a D but not impossible.

What Your Fit Is Telling You

Once you have found your size on the chart, the bra itself confirms whether the cup is right. These are the quick signals; for the full fit check and band adjustments, see how to measure your bra size.

What This Means for You

Cup size is the difference between your bust and your band, one letter per inch. That is the whole calculation, and the chart above turns it into a label in any system you need.

But the letter is a ratio rather than a volume, so it only means something once you anchor it to a band. A 30D and a 38D are both D cups and are genuinely different sizes, which is why the cup letter alone never describes anyone's breasts.

And size is only half of fit. Root width, projection and fullness decide which bra in your size will actually work, which is why a correctly measured size can still fit badly and why changing construction usually helps more than changing size.

Measure with nothing added to the band, re-measure every six to twelve months, and treat your size as a starting point that each brand will interpret slightly differently.

Frequently Asked Questions About Breast & Cup Sizes

This article is for informational and educational purposes and is not medical advice. Sizing varies between brands, styles, and countries, and home measurements are a starting point rather than a guarantee. Volume figures are approximate. For best results, refer to each brand's specific size chart and consider a professional fitting. Any new or unexplained change in breast size, shape, skin or sensation, or a new difference between the two breasts, should be discussed with a doctor. Last reviewed: September 19, 2026.