If you know you wear a 34C but the product page offers S through 3XL, the choice can feel less certain than it should. Start with both parts of your bra size: the number is the band and the letter is the cup. An alpha-size chart combines those two measurements.
Start With Your Current Band and Cup Size
Use a bra that is comfortable on its loosest hook as a reference, then compare its size to the chart on the product page. For many COMFBAY styles, 32B–32DD map to S, 34A–34C map to S, and 34D–34DD map to M. As sizes increase, the same letter size covers a different set of band-and-cup combinations.
The chart is a starting point, not a promise that every style fits identically. Fabric stretch, cup depth, and the level of support you want can change the final choice.
Use Measurements If You Do Not Know Your Bra Size
Measure your underbust firmly around the ribcage, then measure your overbust at the fullest point. The difference between those measurements gives a starting cup range. Keep the tape level around your back, breathe normally, and record both measurements in the same unit. Keep the underbust tape snug without digging in; avoid pressing the bust flatter with the tape. Compare the results with the exact product chart rather than assuming one cup-size formula applies to every brand.
For COMFBAY’s general chart, an underbust of 29–31 inches starts at a 34 band, while 31–33 inches starts at a 36 band. Use the cup difference and the product chart together; do not choose an alpha size from band measurement alone.
When You Land Between Two Letter Sizes
Check what feels wrong before automatically sizing up. If the band digs in, rolls, or makes you want to unfasten it after a few minutes, the larger option may be worth trying. If the band rides up at the back, the issue may be that it is too loose rather than too small.
Then check the cups under a T-shirt. A cup edge that cuts in, gaps, or shifts during normal movement is a better clue than the letter on the tag.
For example, COMFBAY’s general chart places 34C in S and 34D in M. If you usually wear 34C but the S cup cuts in at the top while the M stays smooth without the band moving, that is useful fit information. If M rides up or leaves a clear cup gap, return to S and check the cup shape instead of assuming “larger” is more comfortable.
Do a One-Minute Outfit Check
Put on the top you actually plan to wear. Sit down, reach forward, lift your arms, and stand again. A good size should leave the band roughly level and the cup edge smooth enough that you do not keep adjusting it.
For a lower neckline, the right alpha size still needs to work with the cut of the bra. See our guide to wearing a Deep V neckline without showing your bra before choosing solely by size.
Check the Specific Product Chart Last
Use the chart attached to the exact product as the final decision point. This matters most if you are between sizes, have a fuller bust, or want a firmer fit for a particular outfit. A size chart should make your next step clearer, not make you force an uncomfortable fit.
If you are changing both band and cup at once, read our sister-size guide before choosing a different letter size.
