Bra Size Calculator

Calculate bra size from band and bust measurements. See sister sizes for alternative fit.

By Konstantin Iakovlev · Updated September 2026 · Source: BLS

in
in

Your Size

34C

Band

34

Cup

C

Size Details

Band Size34
Cup SizeC
Full Size34C
Bust − Band Difference3.0 inches

Sister Sizes

Sister sizes have the same cup volume but different band lengths. Try these if your size is unavailable.

Band Down, Cup Up

32D

Your Size

34C

Band Up, Cup Down

36B

Use the Bra Size Calculator above to calculate your results. Enter your values and see instant results — all calculations run in your browser.

Disclaimer: This calculator is for informational purposes only. Results are estimates based on the information you provide and the assumptions described on this page.

How It Works

Finding the right bra size comes down to two measurements: your band and your bust. The payoff for getting it right goes well beyond appearance, since a bra that fits delivers real support and comfort. This tool turns those two numbers into a size you can start shopping with.

Calculation happens in two stages. Your underbust measurement sets the band size: it is rounded to the nearest even number (31 becomes 32, since halves round up), with 28 as the smallest band. The cup then comes from subtracting that band size from your bust measurement, rounded to the nearest inch, with each inch moving up one letter: under half an inch is AA, 1 inch is A, 2 is B, 3 is C, 4 is D, 5 is DD, 6 is DDD/F and 7 is G, up to J at 10 inches or more.

Cup and band sizing shift from brand to brand, which is why trying bras on remains the best confirmation whenever you can. Steer clear of measuring over clothing or letting the tape sit too tight or too loose, as either throws off the result. Treat the size you get here as a strong starting point and let your own comfort make the final call.

Example: Finding Your Perfect Fit

  1. 1 Measure your underbust tightly: 31 inches. Measure your bust at its fullest point: 37 inches.
  2. 2 Band Size Calculation: 31 inches rounds up to a 32 band. Cup Size Calculation: 37 inches (bust) - 32 inches (band) = 5 inches difference.
  3. 3 This results in a calculated bra size of 32DD.
  4. 4 Sister Sizes: If a 32DD isn't comfortable or available, consider trying sister sizes like 34D (one band size up, one cup size down) or 30DDD/F (one band size down, one cup size up), the two the calculator lists, for an alternative fit. These sizes offer a similar cup volume with different band tensions.

Source: BLS · Last updated: September 2026

Frequently Asked Questions

How do I measure my bra size at home?
Measure your underbust snugly for the band size (round to nearest even number) and your bust at the fullest point. The difference in inches determines the cup: 1 inch = A, 2 inches = B, 3 inches = C, 4 inches = D.
What is a sister size in bras?
Sister sizes have the same cup volume with a different band. Going up a band size means going down a cup letter, and vice versa. For example, 34C, 32D, and 36B are all sister sizes with the same cup volume.
Why does my bra size vary between brands?
There is no universal bra sizing standard, so a 34C in one brand may fit like a 32D in another. European brands use centimeters while US brands use inches, adding further variation.

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