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40B bra size — conversions, sister sizes & fit
A 40B fits an underbust of about 87.5–92.5 cm with a bust 11.25–13.75 cm larger than the band. Here is everything that label actually means — and how to check it really fits you.
Your bra size
40B US
Which measurements give 40B?
| cm | |
|---|---|
| Underbust (snug) | 87.5–92.5 |
| Bust (fullest point) | 98.75–106.25 |
| Difference (cup volume) | 11.25–13.75 |
Between two sizes? Measurements near the edges of these ranges can also fit the neighbouring size — check the sister sizes below and, in doubt, trust the fit checks from our measuring guide.
Sister sizes of 40B
38C and 42A hold a similar cup volume to 40B with a tighter or looser band. If the band of a 40B rides up, try 38C; if it digs in, try 42A.
With this profile, fit quality is often the bigger challenge — small cups on standard bands are often cut for a rounder shape than many bodies have, so gaping at the top edge is common. Balconette and demi cuts tend to follow a shallower curve better than full-coverage styles, and a band that stays put matters more than the cup label.
40B in the Cherry Size catalogue In the Cherry Size catalogue, 360 of 617 brands have a recorded size range that includes 40B. That count uses each brand's band range and largest cup (the smallest cup is not recorded) and includes ranges not yet checked. Each of them cuts it differently: the app estimates the size to try at each brand, from your own measurements.In the app, your size is free, and so is your size at 3 brands you choose. Every brand, the fitting room, the wardrobe and the journal need a subscription, with a free trial for eligible new subscribers.
See 40B brand by brand40B in questions
What is 40B in European sizing?
A 40B corresponds to 90B in European sizing and 105B in French/Spanish sizing, by the usual correspondences. The conversion changes the band numbering, and from DD up the cup letter too (US DD = EU E); individual brands can differ.
Is 40B big or small?
It pairs a standard or larger band with a shallower cup. Cup letters mean nothing alone: a cup only has a volume relative to its band, which is why 38C and 42A hold a similar volume to 40B.
My 40B doesn't fit — what should I try?
If the band rides up or feels loose, go to 38C. If the band digs in while the cup is fine, go to 42A. If the cup overflows, try one cup up in the same band; if it wrinkles empty, one cup down. Two minutes with the calculator gives you a fresh estimate.
Nearby sizes
Your size, everywhere you shop
Cherry Size keeps your measurements on your iPhone, translates them into 617 brands, tracks changes through pregnancy, nursing or weight shifts (with a subscription) — and never uploads a thing. In the app, your size is free, and so is your size at 3 brands you choose. Every brand, the fitting room, the wardrobe and the journal need a subscription, with a free trial for eligible new subscribers.
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