A 40 bra size is a band measurement: an underbust of about 35 to 36 inches. It says nothing about the bust until a letter joins it, and the four letters stocked on this band describe four different busts on one frame. This guide covers the band, the letters, and the thing that changes at the top of the range: the places a near-miss fit can escape to start disappearing.
Not sure which letter is yours? The bra size calculator turns two measurements into an answer, sister sizes included.
What the 40 band measures
On Indian sizing the band is your underbust rounded up to an even number, plus four inches, so a 40 band fits an underbust of about 35 to 36 inches (89 to 91 cm). The letter then records the difference between bust and band, starting at A for zero and climbing one letter per inch, with boundaries resolving upward.
UK and US charts build the band without the plus-four, so a 40 band here is a 36 there, and about a 80 in EU sizing. Cup-by-cup equivalents are in the bra size converter.
The four cups on a 40 band
| Size | Bust (inches) | Bust (cm) | Difference |
|---|---|---|---|
| 40A | 40 to 41 | 102 to 104 | 0 to 1 |
| 40B | 41 to 42 | 104 to 107 | 1 to 2 |
| 40C | 42 to 43 | 107 to 109 | 2 to 3 |
| 40D | 43 to 44 | 109 to 112 | 3 to 4 |
Same underbust in every row. And a caution that matters more up here than anywhere else: a letter is a difference, not a volume, and the same letter holds more on a wider band. A 40B contains more than a 34B. Anyone comparing letters across bands is comparing nothing.
Where sister sizes run out
Sister sizes swap band for letter while keeping similar cup volume, and on middle bands they give every size two escape routes. On a 40 they thin out, because band-up lands on 42, which Indian retail rarely makes.
- 40A's single sister is 38B: stocked, ordinary, usable.
- 40B trades down to 38C easily; its band-up sister 42A is mostly theoretical.
- 40C trades down to 38D; 42B is the same story.
- 40D has no practical trade at all: 42C and 38E are both rare rails in India.
So swaps from a 40 band run downward or nowhere. That asymmetry is worth knowing before a fitting room, because it changes what a near-miss means: at 40B a slack band has an easy answer one rail over, while at 40D the answer has to come from the band itself.
Support comes from the band
This is true of every bra and most visible at the wide end: the band provides the large majority of support, and the straps only steady what the band already carries. Every fit complaint on this page routes through that fact. A band that rides up is not supporting; a band that digs is either too small or compensating for a cup too small; straps that groove the shoulders are doing a job the band abandoned. The two-finger test settles it: level all the way round, snug on the loosest hook when new, two flat fingers underneath.
Get the band right and the letter becomes a small, fixable detail. Get it wrong and no letter will save it.
When the outfit removes the band
Backless and deep-cut outfits take the band away entirely, which at this end of the grid is exactly where doubt creeps in. The stocked answer: our strapless adhesive bra runs 30A through 40D, covering every size on this page. Adhesive holds are working hardest at these sizes, so clean dry skin and firm edge pressure stop being tips and start being the difference between an evening that works and one that does not.
The short version
A 40 bra size means a 35-to-36 inch underbust, with the letter recording a zero-to-four inch difference on top, one letter per inch. Letters are differences, not volumes, so cross-band comparisons mislead. Sister-size escapes run downward to 38 or not at all, and the band does nearly all the work, so it gets fitted first and fixed first. The full method is in the bra size chart for India, and the sister sizes guide covers the swaps that do exist.
