A B cup on the Indian chart means your bust measures one to two inches more than your band number. The letter gets called the average size, but a B is a proportion rather than an amount, and it exists on every band from 28 to 40.
Not sure it is your size? The bra size calculator turns two measurements into an answer, sister sizes included.
What does a B cup actually mean?
The Indian chart builds the band from your underbust: round it up to an even number and add four inches. The letter is your bust minus that band number, and B is the second step of six, covering a difference of one to two inches (3 to 5 cm).
The letter never appears alone on a label for a reason. Without a band in front of it, B describes nothing you could check with a tape.
It also reads differently abroad: the body in an Indian 34B is a UK and US 30DD, a 65E in EU sizing. The bra size converter has the full mapping.
B cup measurements, band by band
| Size | Underbust (inches) | Underbust (cm) | Bust (inches) | Bust (cm) |
|---|---|---|---|---|
| 28B | 23 to 24 | 58 to 61 | 29 to 30 | 74 to 76 |
| 30B | 25 to 26 | 64 to 66 | 31 to 32 | 79 to 81 |
| 32B | 27 to 28 | 69 to 71 | 33 to 34 | 84 to 86 |
| 34B | 29 to 30 | 74 to 76 | 35 to 36 | 89 to 91 |
| 36B | 31 to 32 | 79 to 81 | 37 to 38 | 94 to 97 |
| 38B | 33 to 34 | 84 to 86 | 39 to 40 | 99 to 102 |
| 40B | 35 to 36 | 89 to 91 | 41 to 42 | 104 to 107 |
Every row keeps the bust one to two inches (3 to 5 cm) past its band number. The most searched B sizes have their own pages: 32B and 36B.
Is a B cup average?
"Average" treats bust size as one number line with B parked in the middle. A bra size is two numbers, a ribcage and a bust, and they move independently; the word compresses both into one syllable and keeps neither. The table above holds seven different bodies. A 28B is a bust of 29 to 30 inches. A 40B is a bust of 41 to 42. If one of them is average, the other is not, and the letter cannot tell you which.
The letter does not even pin down one cup volume. Each letter is measured against its own band, so a B on a 40 band holds noticeably more than a B on a 28. Two people can both wear B, look visibly different, and both be fitted correctly. What they share is a one to two inch difference, and nothing else.
What are the sister sizes for a B cup?
B sits far enough up the scale to have sisters in both directions everywhere. In the middle of the chart both are stocked: 34A ← 32B → 30C, the looser band to the left, the tighter to the right, all three holding about the same.
- Band rides up, cup fits: band down and letter up (a 32B moves to 30C)
- Band digs in, cup fits: band up and letter down (a 32B moves to 34A)
- Band fine, cup spilling: a letter problem, not a band problem. Go 32C, same band.
At the edges of the range one direction usually leads off the shelf: a 30B's band-down sister is 28C (unstocked), and a 40B's band-up sister is 42A (unstocked). The chart in bra sister sizes marks every pair.
Where the letter actually matters
The band decides how a bra grips; the letter decides how much the cup holds. The letter carries the most weight when you buy something shaped as a cup with no hooks or straps to adjust afterwards, and an adhesive bra is the clean example: you order it by your ordinary band and letter, and the moulded cup either matches your volume or it does not. At B the maths is kind, because a moderate cup weight is the easiest load for an adhesive to hold. Our strapless adhesive bra runs 30A to 40D, which covers every band in the table except 28; a 28B reaches the grid through its sister size, 30A.
The short version
A B cup is a bust one to two inches above the band number, on whatever band it sits. Calling it average compresses two measurements into one word and loses both. The same letter holds different amounts on different bands, so a 28B and a 40B share a difference and nothing else. The method behind the table is in the bra size chart for India, and the bra size calculator does the working for you.
