For every band and cup in one grid, use the bra size chart. This page explains what the letters mean.
What a cup letter measures
Bra cup size is not a fixed volume. It is a difference. Take the bust measurement at the fullest point, subtract the snug underbust that sets the band, and count the inches. Each inch moves you one letter along. A difference of 3 inches is a C, whatever the band.
That is why the letter never travels alone. A size is always band plus cup, such as 34C. The band tells you the frame. The cup tells you how much the bust projects from it.
The letter order, inch by inch
In UK sizing, the cups run in this order, one inch per step:
AA, A, B, C, D, DD, E, F, FF, G, GG, H, HH, J, JJ, K.
So a difference of 5 inches is DD and 6 inches is E. Each double letter counts as a full step of its own, not a half step. The chart above shows these steps against every band, with the other countries alongside.
Each letter in detail
The most-searched letters each have their own page, with measurements for every band from 28 to 44 and their sister sizes:
- What is a B cup? 2 inches of difference, and why it is often a misfit 34B.
- What is a C cup? 3 inches, and whether C is still average.
- What is a D cup? 4 inches, and where the “D is big” myth comes from.
- What is a DD cup? 5 inches, and why Europe calls it E.
- What is an E cup? The letter that means three different cups depending on the brand’s country.
How the letters differ by country
Up to DD, US, UK and Australian letters match. After that each system has its own habits:
- UK uses doubles: DD, E, F, FF, G, GG.
- US often writes the next steps as DDD and then G, H, I. The UK E is a US DDD. The UK F is a US G, and the UK FF is a US H.
- Australia mostly follows the UK letters, though some local brands skip the doubles above DD.
- EU and France use single letters in order. The UK DD is an EU E, the UK E is an EU F, and the UK F is an EU G.
US letters above DDD are the least consistent of all. Some brands use DDDD, some jump to G. When you are past DDD, the brand’s own chart beats any general rule.
European cups are also defined in centimeters. One EU cup step is about 2 cm of difference between bust and band, a little less than an inch. For everyday sizes the conversion lines up well. At the larger end, small differences between brands become more noticeable.
Same letter, different volume
Because a cup is relative to the band, the same letter holds different amounts on different bands. A 30E holds far less than a 38E. Moving up two band sizes while keeping the letter makes the cups noticeably larger, not just the band.
It also works the other way. A 32DD, a 34D and a 36C hold roughly the same volume. Each moves the band one size and the cup one letter in the opposite direction. These are sister sizes, and they are handy when a band feels wrong but the cups feel right.
Common myths about cup size
- “D is the large size.” A D is just 4 inches of difference. The older habit of adding 4 inches to the band tends to put people in loose bands with cups that are too small, which makes D sound bigger than it is.
- “Cup letters are the same everywhere.” They match only up to DD. After that, compare systems with the bra size chart.
- “If the cup spills, buy a bigger band.” A bigger band also makes the cups bigger, but the band then gives less support. Going up a cup on the same band is usually the better fix.
- “Gaping means the cup is too big.” Sometimes. It can also mean the cup shape is wrong for the breast shape. Molded cups are stiff, and an unlined, seamed cup often fits natural shapes better.
How to find your cup size
Measure the snug underbust and the standing bust, and if you can, a leaning bust as well. The how to measure bra size guide walks through each step. Enter the numbers in the calculator and it gives you the band and cup in your country’s sizing.
If you already own a bra that fits well, its label is the next best source. Read the cup from the tag and convert it with the chart. Then do a quick how a bra should fit on any new bra, because the letter is a starting point and the fit is the final answer.
For the whole system in one place, band, cup, sister sizes and countries, read how bra sizes work. Curious where the scale ends, or what’s typical? See the biggest bra size and the average bra size.
Sources & method: sizing rules follow the standard band-and-cup system used by UK, US, AU and EU brands, checked against fitting guides from specialist retailers and fitting communities. How we work.