A bra cup size is the difference between the bust and the band measurement, and in US and UK sizing each 1-inch step in that difference moves the cup up one letter: 1 inch is an A, 2 inches a B, 3 inches a C, 4 inches a D. European sizing does the same thing in 2 cm steps. The catch is that a cup letter is never a fixed volume. A 32D and a 38D hold very different amounts, which is why a cup, a pad or an underwire only makes sense when it's read together with the band.
Key Takeaways
Cup size = bust minus band. One cup letter per 1 inch (US/UK) or per 2 cm (EU).
A cup letter is relative to the band: 32D, 34C and 36B are sister sizes with roughly the same cup volume.
Letters split after D: US goes DD, DDD/F, G; UK goes DD, E, F, FF, G. The same letter can mean two different cups.
EU bands are underbust in cm (70, 75, 80); French and Spanish bands run 15 higher; Australian bands use dress-size numbers (10, 12, 14).
What Are Bra Cup Sizes?
A bra size has two parts: a number for the band and a letter for the cup, and bra cup sizes are based on the difference between the bust and band measurements, not on a fixed breast volume. The band is the measurement around the ribcage just under the bust. The cup letter describes how much larger the bust is than that band, so it is a ratio, not an absolute size: in US and UK sizing, each inch of difference typically maps to a cup letter, so 1 inch is A, 2 inches is B, and "34C" means a 34-inch band with a bust about 3 inches larger. In European sizing, cup sizes usually increase in 2 cm steps.
For lingerie brands, bra manufacturers, fitters, and consumers trying to measure correctly, compare sizes, or convert between systems, that difference affects fit, comfort, and consistency across brands and markets, especially when sourcing from a large global garment accessories supplier. A better fit means better support and fewer problems like shoulder grooves, back pain, and the confusion caused by brand and regional sizing differences. Sizing charts, pattern grading, cup molds, and other bra components all have to follow the full band-plus-cup combination.
Bra Cup Size Chart: How Many Inches Is Each Cup?
Each additional inch between bust and band adds one cup letter in US and UK sizing, but band and cup sizes vary across brands, especially for larger cup sizes, and cup size increases are not perfectly standardized. The first four letters match across systems. After D, the US and UK diverge, and that's where most size confusion between brands and markets starts.
Bust minus band | US cup | UK cup | EU cup (cm difference) |
|---|---|---|---|
Under 1 in | AA | AA | AA (10-12 cm) |
1 in | A | A | A (12-14 cm) |
2 in | B | B | B (14-16 cm) |
3 in | C | C | C (16-18 cm) |
4 in | D | D | D (18-20 cm) |
5 in | DD / E | DD | E (20-22 cm) |
6 in | DDD / F | E | F (22-24 cm) |
7 in | G | F | G (24-26 cm) |
8 in | H | FF | H (26-28 cm) |
9 in | I | G | I (28-30 cm) |
Brands vary, especially above D. Always check which system a label size or spec sheet follows, since sizing can shift from one manufacturer to another and across different countries, so it often gives only an approximate fit.
Notice the drift: by 7 inches, the US calls it a G while the UK calls it an F, and an H cup is a good example of how the letters split further as sizes increase. A lingerie range sold into both markets needs its labels and size charts mapped carefully, or a "DD" that fits in London won't match a "DD" in New York for long once the sizes climb.
How Do You Measure Bra Size?
Two measurements give a starting size: the underbust circumference and bust measurement. Take them standing straight, with the tape level and parallel to the floor around the chest and body. The underbust should be snug, since the bra band provides about 80% of the support while the straps provide about 20%.
Band: measure snugly around the rib cage directly under the bust. Band sizes typically start at 30 and increase by twos. Many modern fitters skip that step and use the underbust rounded to the nearest even number, which usually gives a firmer band and a larger cup letter. The band and cup both matter because brands size them differently. If the band rides up, it is too big; it should fit snugly, not feel loose, and stay level while wearing the bra.
Bust: measure loosely around the fullest part of the bust size. The bust circumference is taken around the breasts at their fullest point, usually across the nipples. Subtract the band size; the difference in inches is the cup letter from the chart above. For example, a one inch difference is an A cup, a two inch difference is a b cup, and a three inch difference is a C cup. The bra cups should fully contain breast tissue without spilling or gaping.
The bra's center panel should lie flat against the sternum, and the underwire should encircle breast tissue without discomfort. Many women are put in the wrong size, and about 80% of department store fittings result in poor fit.
A flexible tailor's tape measure with both inch and centimeter scales makes it easy to work in either system. A common mistake is also the most common mistake: choosing a too large band with too small a cup.
How Do Bra Sizes Convert Between US, UK, EU, FR and AU?
Bra sizing isn't international, so the same person can get different results from the same label size in different countries. US and UK bands are in inches, EU bands are the underbust in centimeters in 5 cm steps, French and Spanish bands run 15 cm higher than the EU number, and Australian and New Zealand bands borrow dress-size numbers. The band is usually what trips people up, not the cup.
US / UK band | EU band | FR / ES band | AU / NZ band |
|---|---|---|---|
30 | 65 | 80 | 8 |
32 | 70 | 85 | 10 |
34 | 75 | 90 | 12 |
36 | 80 | 95 | 14 |
38 | 85 | 100 | 16 |
40 | 90 | 105 | 18 |
42 | 95 | 110 | 20 |
So a US 34C is a 75C in Germany, a 90C in France and a 12C in Australia. Above D, convert the cup letter using the cup chart as well, because a UK 34E is not the same cup as an EU 75E, and the same careful check applies with an H cup across different systems.
Cup Sizing at MH: Pads, Wires and Trims Graded to the Same Chart
MH (Ningbo MH), founded in 1999 and supplying buyers in more than 150 countries, stocks lingerie pads in triangle, round, half-round and molded-cup shapes alongside the underwires, hooks and eyes, straps, elastic, lace and thread that finish the bra, drawn from roughly 10,000 garment accessories and tailoring materials.
Across a full size grid, consistency matters as much as range. With 9 factories covering about 350,000 m², a 3,000+ workforce and 2,000+ partner manufacturers, MH can repeat the same pad shape, thickness and size run season after season for lingerie brands, bra manufacturers and swimwear makers, as well as scale specialized lines like 150D/2 rayon embroidery thread for coordinated lingerie detailing. Browse the full range of lingerie accessories or contact MH with the shape, size run and thickness you need.
Frequently Asked Questions
How many inches is each bra cup size?
Each cup letter is about 1 inch of difference between the bust and the band in US and UK sizing: A is 1 inch, B is 2, C is 3, D is 4—the starting point for a perfect fit, though brand variation still matters. European sizing uses 2 cm steps instead. After D, US and UK letters diverge, so a 6-inch difference is a US DDD/F but a UK E.
Is a D cup the same size on every band?
No. A cup letter only describes the difference between bust and band, so the actual volume grows with the band. A 38D holds noticeably more than a 32D. The same letter does not mean the same cup bra volume or shape on every band. A 32D is closer in volume to a 34C or 36B, which are its sister sizes.
What are bra sister sizes?
Sister sizes share the same cup volume on a different band. Go down one band and up one cup letter, or up one band and down one cup. For example, 32D, 34C and 36B are sister sizes. They usually share the same underwire size, which is why one cup mold can often cover several of them.
How do I convert US bra sizes to EU sizes?
Convert the band first: US 32 is EU 70, US 34 is EU 75, US 36 is EU 80, adding 5 cm per step. French and Spanish bands are 15 higher than EU, so a US 34 is an FR 90. Cups match through D; above D, use a cup chart because EU letters follow 2 cm steps.
Is DD the same as E?
It depends on the system. A bra's style label doesn't override the sizing system, so checking the system matters more than relying on the label alone. In US sizing, DD and E usually mean the same cup, one step above D. In UK sizing, DD comes first and E is the next cup up. In EU sizing there's no DD, so E directly follows D. Check which system a brand uses before comparing.
Conclusion
Bra cup sizes come down to one ratio: bust minus band, one letter per inch or per 2 cm. About 70-85% of women wear incorrectly fitted bras. Around 25% struggle to find a properly fitted bra. For lingerie brands and bra manufacturers, the practical lesson is that a cup letter never stands alone. Read it with the band and the sizing system to get closer to the perfect bra and a more natural fit. Breast shape matters too, including each person's unique shape and asymmetric breasts, because the right style has to match the body rather than the size alone, and breast volume can change with weight over time.