How a breast size chart works
A breast size chart maps the difference between your bust and band measurements to a cup size. Measure around the fullest part of your bust, measure your ribcage just under the bust, and subtract the second from the first. Each inch of difference equals one cup size — 1 inch is an A, 2 a B, 3 a C, 4 a D, 5 a DD, 6 a DDD (US) or E (UK). Cup size measures volume relative to your ribcage, so it's always paired with a band number to make a full size like 34C. The chart below shows every cup size with its measurement and US/UK/EU label.
Below you'll find the complete cup size chart, a visual guide to how volume changes across sizes, a note on average and most-common sizes, and a free calculator that turns your two measurements into your cup size across systems. Cup size is only ever half of a bra size, though — so for the full fitting workflow, including band fit and how to measure properly, we'll point you to our bra size chart and calculator.
Every Cup Size, Beautifully Made
From A to H and beyond — HauteFlair carries structured, well-graded bras across the full cup range and every band. Filter to your size and shop styles built to fit.
Shop All Bras → Calculate My Cup Size →- Cup size = bust measurement minus band measurement, in inches.
- Each 1 inch of difference = one cup size (1″ = A, 2″ = B, 3″ = C, 4″ = D, 5″ = DD).
- Cup size measures volume relative to the band — a 30D and a 38D differ despite the shared letter.
- US and UK match through DD, then diverge: 6″ = DDD (US) or E (UK).
- The average US bra size is commonly cited around 34DD.
- Always pair the cup letter with a band number for a full size like 34C.
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.
| Bust − band difference | US cup | UK cup | EU cup | Relative volume |
|---|---|---|---|---|
| Under 1 in (under 2.5 cm) | AA | AA | AA | Smallest |
| 1 in (2.5 cm) | A | A | A | Small |
| 2 in (5 cm) | B | B | B | Small–medium |
| 3 in (7.5 cm) | C | C | C | Medium |
| 4 in (10 cm) | D | D | D | Medium–full |
| 5 in (13 cm) | DD | DD | E | Full |
| 6 in (15 cm) | DDD | E | F | Full |
| 7 in (18 cm) | DDDD / G | F | G | Very full |
| 8 in (20 cm) | G / H | FF | H | Very full |
| 9 in (23 cm) | H / I | G | I | Fullest |
A complete bra size pairs this cup letter with your band number (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.
A cup letter is not a fixed breast size — it's a ratio. The same letter holds more volume on a bigger band, so a 30D and a 38D are both "D cups" but genuinely different sizes. That's why "I'm a C" doesn't fully describe anyone's breasts; the band-and-cup combination does. Read the chart for the letter, then anchor it to your band.
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):
| Cup (US) | Difference | Approx. volume at 34 band |
|---|---|---|
| AA | <1 in | ~180 mL (cc) |
| A | 1 in | ~230 mL (cc) |
| B | 2 in | ~290 mL (cc) |
| C | 3 in | ~340 mL (cc) |
| D | 4 in | ~400 mL (cc) |
| DD | 5 in | ~460 mL (cc) |
| DDD (UK E) | 6 in | ~510 mL (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's the chart above, done for you. Switch between inches and centimeters as needed.
Find Your Cup Size
Enter your underbust (band) and full bust. The result leads with US sizing; your UK, EU, French, Australian, and Japanese cup labels appear in the tiles, with sister sizes below.
How to Measure for the Chart
The chart only works with two accurate numbers. Here's the quick version; for the full method, band-fit checks, and sister sizing, see our complete how to measure your bra size guide.
Band, Then Bust
Band: wrap a soft tape around your ribcage directly under the bust, level and snug. Round to the nearest even number — that's your band size.
Bust: wrap the tape around the fullest part of the bust, parallel to the floor, without compressing. Subtract the band from this number.
The difference is your cup, by the chart above. A 34-inch band with a 38-inch bust is a 4-inch difference — a D cup — so a 34D.
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 — note that EU sizing uses single letters throughout, so it runs one letter ahead of the UK from DD upward.
| Difference | US | UK | EU |
|---|---|---|---|
| 4″ | D | D | D |
| 5″ | DD | DD | E |
| 6″ | DDD | E | F |
| 7″ | DDDD / G | F | G |
| 8″ | G / H | FF | H |
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.
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" isn't 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.
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. Cup size is also relative to the band, so an "average" cup letter still means different volumes on different frames.
"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
What Your Fit Is Telling You
Once you've 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 you notice | What it usually means | Try |
|---|---|---|
| Breast spills over the top or sides | Cup is too small for your volume | Same band, one cup up (e.g. 34C → 34D) |
| Cup wrinkles or gapes at the top | Cup is too large | Same band, one cup down (e.g. 34D → 34C) |
| Band rides up your back | Band too loose — not a cup problem | Smaller band, one cup up (sister size) |
| Looks right but the size feels "off" between brands | Cup letter is correct; brand grading differs | Try a sister size in that brand |
Frequently Asked Questions About Breast & Cup Sizes
How do you read a breast size chart?
What is the average breast size?
Does cup size mean breast size?
How is cup size measured?
What are the cup sizes in order from smallest to largest?
Is cup size the same in US and UK sizing?
How much volume does each cup size hold?
What is the most common cup size?
Can my cup size change?
What does the cup letter tell me when I shop?
This article is for informational and educational purposes. 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. Last reviewed: May 25, 2026.
