A US bra size chart turns two numbers into one size, and that size is simpler than it looks. A US bra size is a band number plus a cup letter. The band number comes from the measurement around your ribcage, and the cup letter comes from the difference between your bust measurement and your band measurement. Learn those two numbers, find the difference, and the chart below does the rest.
This chart is a starting point, not a guarantee. Brands cut differently, styles fit differently, and your own try on decides the final size.
Jump to: The two measurements | How to read the chart | Worked examples | Sister sizes | US versus UK | Why sizes differ | Fit checks | Between sizes | FAQs
The Two Measurements Brands Ask For
Brands ask for two measurements because each one sets a different part of the size. The underbust measurement sets the band. The bust measurement, compared with the band, sets the cup.
Take the underbust measurement around your ribcage, directly under your bust, with the tape snug and level. That number, rounded to the nearest even band size, is your starting band.
Take the bust measurement around the fullest part of your bust, with the tape level and not pulled tight. The difference between this number and your band number gives your cup.
If you want a calculator to do the subtraction, the Stellaleah bra size calculator uses the same two inputs. For a fuller walkthrough, see How to Calculate Your Proper Bra Size.
Do not treat the cup letter on its own as a size. A D cup on a 32 band holds far less volume than a D cup on a 40 band. The letter only means something with its band number.
How to Read the US Bra Size Chart
Read the chart in two steps. First, find your band row. Second, find your cup from the inch difference between your bust and band measurements. Each cup step stands for one inch of difference. That one inch per letter rule is the convention Bare Necessities describes when it explains subtracting band from bust. Wacoal uses the same logic: band from the underbust, cup from the bust minus underbust difference.
| Bust minus band difference | US cup |
|---|---|
| Less than 1 inch | AA |
| 1 inch | A |
| 2 inches | B |
| 3 inches | C |
| 4 inches | D |
| 5 inches | DD |
| 6 inches | DDD |
| 7 inches | G |
If your difference falls between whole inches, round to the nearest whole inch for a first try, and let the fit checks below settle the final size.
Now put band and cup together in the full grid. Find your band row, move across to your cup, and you have a complete US size.
| Band | AA | A | B | C | D | DD | DDD | G |
|---|---|---|---|---|---|---|---|---|
| 30 | 30AA | 30A | 30B | 30C | 30D | 30DD | 30DDD | 30G |
| 32 | 32AA | 32A | 32B | 32C | 32D | 32DD | 32DDD | 32G |
| 34 | 34AA | 34A | 34B | 34C | 34D | 34DD | 34DDD | 34G |
| 36 | 36AA | 36A | 36B | 36C | 36D | 36DD | 36DDD | 36G |
| 38 | 38AA | 38A | 38B | 38C | 38D | 38DD | 38DDD | 38G |
| 40 | 40AA | 40A | 40B | 40C | 40D | 40DD | 40DDD | 40G |
| 42 | 42AA | 42A | 42B | 42C | 42D | 42DD | 42DDD | 42G |
| 44 | 44AA | 44A | 44B | 44C | 44D | 44DD | 44DDD | 44G |
Not every brand makes every cell in this grid. A brand may stop at DDD or skip smaller bands. The grid shows how the system works, not a promise that every size exists in every style.
Two Worked Examples
Example 1: how a 34C is calculated. Suppose your underbust gives a 34 band and your bust is 37 inches. Subtract: 37 minus 34 equals 3. A 3 inch difference is a C cup, so your starting size is 34C. Band first, difference second, letter last.
Example 2: sister sizes for that same 34C. Suppose the 34C cups fit well but the band feels loose. Its sister sizes are 32D (one band down, one cup up) and 36B (one band up, one cup down). Both hold roughly the same cup volume as 34C, because each band step trades against one cup step.
Sister Sizes Explained
Sister sizes are different labels for about the same cup volume. Move one band size down and one cup letter up, or one band size up and one cup letter down.
Use a sister size to fix a band problem, not a cup problem. If the cups gape or spill, the cup volume itself needs to change, not just the label.
Sister sizes are close, not identical. Cup shape, wire width, and band stretch still change between sizes.
US Versus UK Naming Differences
US and UK sizes agree up to DD, then the letters part ways. A US DD is a UK DD, so nothing changes at that step. After that, the systems diverge.
In the standard US ladder, the sequence runs D, DD, DDD, then G. In the UK ladder, the same volumes run D, DD, E, F, FF, then G.
So a US DDD equals a UK E, and a US G equals a UK F in the standard mapping. Some US brands skip DDD and print F instead, and some use their own ladders, so always check a brand’s chart for sizes above DD.
Always check the brand’s own cup ladder before converting above DD. The letters look familiar, which is exactly why they mislead. For a full side by side conversion, see UK, US, and EU Bra Size Conversion.
Why the Same Labeled Size Fits Differently Across Brands and Styles
A labeled size is a starting point because brands do not share one pattern. One brand’s 36D may run snug while another’s runs roomy, and the same brand may cut a balconette differently from a T shirt bra.
Style matters just as much as brand. A molded T shirt bra, a seamed balconette, and a minimizer can all fit the same labeled size differently, because each shapes the cup in its own way. Breast shape plays a part too, changing which cup shape works. The Breast Shape and Bra Fit Guide explains how shape, not just size, changes the best style to try.
If one brand’s size fails, do not assume the chart failed. Try the same size in a different style first, then try a sister size or one cup up or down.
Fit Checks Once You Try a Size
Try the size on the loosest hook first. A new band should feel snug there, so you have tighter hooks left as the elastic relaxes with wear. Fasten it, adjust the straps, and check four things.
Band level. The band should sit level all the way around, front and back. A band that rides up in back is usually too loose, and the fix is often one band size down with one cup size up.
Cups contain without gaps or spilling. The cups should hold the full bust with a smooth line at the top edge. Gaping usually means the cup is too large or the wrong shape, while spilling usually means the cup is too small.
Center front sits flat. The small panel between the cups should rest against your breastbone. If it floats away from the body, the cups are usually too small.
Straps stay put. Straps should stay on the shoulders without digging in and without slipping off. Straps are not meant to do the heavy lifting. If tightening them is the only way to get support, the band is probably too loose.
What to Do Between Sizes
Between sizes is normal, and the best move depends on which part is between. If the band feels between sizes, try the smaller band first, since bands stretch. If the cup feels between sizes, try the larger cup first, since slight room is easier to live with than spilling.
Try both neighbours before you decide. Try the chart size plus one cup up and one cup down in the same style, if you can. Comparing all three beats guessing from memory, and it often reveals that shape, not size, was the real issue.
If you are shopping for a teen, use the parent guides instead of this adult chart: How to Talk to Your Daughter About Bras and Bra Shopping Checklist for Parents.
Frequently Asked Questions
What is a US bra size, in plain terms?
A US bra size is a band number plus a cup letter. The number is the band around your ribcage, and the letter stands for the inch difference between your bust and your band.
How do I use a US bra size chart?
Find your band row, then find your cup from the difference between your bust and band measurements. 1 inch difference is A, 2 inches is B, 3 inches is C, 4 inches is D, 5 inches is DD, 6 inches is DDD, and 7 inches is G.
What is the difference between US DD and US DDD?
DD is a 5 inch difference and DDD is a 6 inch difference. DDD is one cup larger than DD on the same band, and in UK letters a US DDD usually corresponds to a UK E.
What is my sister size?
Your sister sizes sit one band step away in each direction, with the cup letter moved the opposite way. For a 34C, the sister sizes are 32D and 36B. They hold roughly the same cup volume with a tighter or looser band.
Why does my size change between brands?
Brands cut to different patterns, and styles shape the cup differently. Your chart size is a starting point, and the brand’s own chart plus a try on decide the final size. A change of one band or one cup between brands is common.
Should I round up or down between sizes?
For the band, try the smaller size first, since bands stretch with wear. For the cup, try the larger size first if you are spilling, and the smaller size first if you are gaping.
Your Next Step
Start with your chart size, then try it on. Check the band level, the cup line, the center front, and the straps, and move one step at a time from there. If the cups fit but the band does not, try a sister size.
If the label above DD looks unfamiliar, check that brand’s cup ladder before you order. The chart gets you close. The fitting room gets you the rest of the way.
