Bra Size Calculator
Estimate your bra band size and cup size from your underbust and bust measurements in inches.
- Underbust (Band)32 in
- Bust (Fullest Point)36 in
The 4 in gap between your bust and underbust measurements is what determines the D cup letter — a bigger gap means a bigger cup.
ƒShow your work
- 1Band size rounds your 32 in underbust to the nearest even number = 32
- 2Bust minus underbust = 36 − 32 = 4 in difference
- 3Each inch of difference steps up one cup letter (0"=AA, 1"=A, 2"=B, ...) → 4" = D cup
- 4Estimated size: 32D
About the Bra Size Calculator
This calculator estimates a bra size from two tape-measure numbers: your band measurement (snug, directly under the bust) and your bust measurement (around the fullest point). It's the same band-and-cup math used behind the counter at a fitting appointment, just without needing to book one.
People usually pull this up after a weight change, after a bra stops fitting the way it used to, or when shopping online somewhere without a fitting room — a size estimate up front saves a round of returns. It's also a common first stop for someone buying their first bra and unsure where to even start.
Because it's just a bit of arithmetic on two numbers you already typed in, everything runs locally in your browser — there's no account, no measurement history saved anywhere, and nothing about your body leaves your device.
How it’s calculated
The band size rounds your underbust measurement to the nearest even number, which is how bra bands are conventionally sized. The cup size comes from the difference between your bust and underbust measurements: each full inch of difference steps up one cup letter, starting at AA for a 0" difference, A for 1", B for 2", and so on.
Frequently asked questions
How do I measure for band and bust size at home?
Measure the band snugly around your ribcage directly under your bust, keeping the tape level and parallel to the floor. Measure the bust around the fullest part while wearing an unpadded bra, then let the difference between the two numbers determine your cup size.
Why did I get a different size than what I usually buy?
Sizing isn't standardized across brands — a cut that runs small in one label can run large in another, and this calculator gives a starting estimate rather than a guaranteed fit. Treat the result as a size to try on or order first, not a final answer.
What if my measurement falls between two even band numbers?
Round to the nearest even number, which is the convention most brands use for band sizing — an odd measurement like 33 inches typically rounds to a 34 band.
Does this account for sister sizing?
Not directly. Sister sizes (the same cup volume in an adjacent band size, like 34C and 36B) are a separate concept from this estimate — if the calculated size doesn't fit right, trying the sister size up or down in band with the opposite cup direction is a common next step.
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