Bra Size Calculator

A Bra Size Calculator is a helpful tool designed to estimate your correct bra size by using simple body measurements such as the band size (underbust) and the bust size (fullest part of the chest). By entering these values, the calculator determines both the band and cup size, giving you a more accurate fit compared to guessing or relying on standard sizes.

Free

Instant results

Runs in your browser

How it works

Bra size is two measurements: the band, which goes around the ribcage under the bust, and the cup, which is the difference between the bust measurement and the band.

Measure snugly under the bust, level all the way round — that is the band.
Measure loosely around the fullest part of the bust.
Subtract the band from the bust: each inch of difference is one cup size (1 in = A, 2 in = B, 3 in = C, and so on).

Difference to cup size
Bust − band	Cup (US)	Cup (UK)
1 in	A	A
2 in	B	B
3 in	C	C
4 in	D	D
5 in	DD	DD
6 in	DDD / F	E
7 in	G	F
8 in	H	FF

Sizes are given for the US, UK and EU, which label the larger cups differently. Above a D cup the letters diverge, so a US 34DDD is a UK 34E — check which system a label uses before buying.

Examples

Worked examples:

Band 32 in, bust 35 in: 3 in difference — 32C.
Band 34 in, bust 40 in: 6 in — 34DDD in the US, 34E in the UK.
Band 30 in, bust 31 in: 1 in — 30A.

Sister sizes hold the cup volume while changing the band: 34C, 32D and 36B all fit a similar bust. If the band rides up, go down a band and up a cup.

Bra Size Calculator: frequently asked questions

How do I measure my bra size at home?

Use a soft tape: measure your underbust (snug, level) for the band, then your bust at the fullest point. Subtract band from bust to get the cup.

What does 34C mean?

A 34-inch band with a 3-inch difference between bust and band (C cup).

What is a sister size?

A size with the same cup volume on a different band: go down a band and up a cup (34C → 32D) or the reverse (34C → 36B).