A 34B bra has a 34-inch band and a B cup, which means your bust measures about 2 inches more than your band. With our measuring method that works out to an underbust of just over 32 up to 34 inches and a bust of roughly 36 inches.
| Band 34 | Underbust over 32 and up to 34 inches (81–86 cm). We round your underbust up to the next even number. |
|---|---|
| Cup B | Bust about 2 inches bigger than the band: roughly 35½ to 36½ inches (90–93 cm) around the fullest part. |
| Sister sizes | 32C (tighter band) and 36A (looser band). Full diagonal: 28DD, 30D, 32C, 34B, 36A, 38AA. |
| Same size abroad | UK 34B · EU 75B · French 90B · Australia / NZ 12B |
Brands measure differently, and some US brands add inches to the band. Use these numbers as a starting point, then check the fit. Calculate your own size · See every sister size · Convert another size
What does 34B mean?
The number and the letter measure two different things. 34 is the band, the part that wraps around your ribcage and does most of the lifting. B is the cup, and it only means something next to the band. Each cup letter adds about an inch of difference between your bust and your band: A is 1 inch, B is 2, C is 3, and so on.
That is why a B cup isn’t a fixed amount of breast tissue. A 34B holds more than a 32B and less than a 36B, even though all three share the letter B. The bra size chart shows every band and cup step side by side.
What measurements give you a 34B?
You get a 34B when your snug underbust measurement lands just over 32 up to 34 inches and your bust is 2 inches bigger than the band. Here’s how two quick tape measurements turn into the size:
- Measure snugly around your ribcage, directly under your bust. Round up to the next even number. Anything from 32¼ to 34 inches gives a 34 band.
- Measure loosely around the fullest part of your bust, standing straight. Round to the nearest whole inch.
- Subtract the band from the bust. A difference of 2 inches is a B cup, so 36 − 34 = B.
Our guide to measuring your bra size covers where to hold the tape and the mistakes that throw the numbers off.
Why your store size might not be 34B
Some US brands still add 4 or 5 inches to the underbust to get the band. Someone with a 30-inch underbust and a 36-inch bust might be sold a 34B under that rule, while our method gives 30DDD (UK 30E). That’s a big gap: the 34B band is 4 inches looser, and its cups are two sizes smaller than the 30DDD’s. The cup volume of a 30DDD on a 34 band would be a 34D, not a 34B. If you’ve worn 34B for years and the band creeps up your back, this is the most common reason.
What are the sister sizes of 34B?
The sister sizes of 34B are 32C and 36A. A sister size keeps roughly the same cup volume while changing the band, so you go down a band and up a cup, or up a band and down a cup.
- 32C: same cups, tighter band. Try it if your 34B band rides up or you’re already on the tightest hook.
- 36A: same cups, looser band. Try it if the band digs in even on the loosest hook.
Sister sizing fixes band problems. It won’t fix cups that are simply the wrong shape for you, so check the style too. You can work out any size’s family with our sister size calculator.
How should a 34B fit?
A 34B fits well when the band sits level and firm, the cups lie smooth, and the center panel between the cups touches your chest. Run through these checks in front of a mirror:
- Band: level all the way round, snug on the loosest hook. You should fit two fingers under it, not a whole hand.
- Cups: no spilling over the top or sides, and no empty gaps or wrinkles.
- Center gore: lies flat against your breastbone in an underwired bra.
- Straps: stay put without digging in. They should carry only a small share of the weight.
If something feels off, our bra fit checker walks you through the likely cause.
Signs 34B isn’t your size
The fix depends on where the problem shows up:
| What you notice | Likely cause | Size to try |
|---|---|---|
| Band rides up your back | Band too loose | 32C |
| Breast tissue spills over the cup edge | Cup too small | 34C |
| Cups wrinkle or gape at the top | Cup too big or the wrong shape | 34A, or a different style |
| Band digs in on the loosest hook | Band too tight | 36A |
Try one change at a time. Moving the band and the cup at once makes it hard to tell what helped.
Which bra styles suit a 34B?
B cups have more choice than almost any other size, because nearly every brand and style starts at or below B. Soma, Wacoal and Victoria’s Secret all list B cups in their standard ranges. That means you can pick by outfit rather than by what’s available:
- T-shirt bras for a smooth line under fitted tops. See our guide to the T-shirt bra.
- Balconette and demi bras for a lower, wider neckline.
- Bralettes and wireless bras for comfort on lighter days, since B cups usually need less structure.
- Push-up and plunge bras if you want more lift or cleavage under a low neckline.
Shopping for 34B
Affiliate links-
34B T-shirt bras
Molded, seamless cups for everyday wear. Look for a band that is firm on the loosest hook.
Search Amazon for 34b t-shirt bras (opens in a new tab, affiliate link) -
34B wireless bras
Soft support without a wire. Check that the band is wide enough to stay level.
Search Amazon for 34b wireless bras (opens in a new tab, affiliate link) -
34B bralettes
Light support for lounging. Choose a lined bralette if you want more coverage.
Search Amazon for 34b bralettes (opens in a new tab, affiliate link) -
34B push-up bras
Angled padding for lift. Make sure the center gore still touches your chest.
Search Amazon for 34b push-up bras (opens in a new tab, affiliate link)
Results are Amazon’s, not our picks. Check the size range, the return policy and the features above before you buy.
Is 34B the same in every brand?
No, so treat 34B as your starting point rather than a guarantee. Bands stretch differently, cups are cut for different shapes, and brands use different measuring rules. Soma’s own chart, for example, maps some underbust measurements to a larger band than ours does. When you try a new brand, check its size chart and try your sister sizes if the first bra doesn’t sit right. Our brand size guides compare how popular brands label and measure.
