Bra Size Calculator
Convert bust and band measurements into US, UK, EU, and Australian bra sizes.
Written by Golam Rabbani, Founder & Lead Engineer — Last updated 2026-05-01
How to use this bra size calculator
- Measure under your bust and enter that number in the Band Size field (in inches).
- Measure around the fullest part of your bust and enter it in the Bust field.
- Press Calculate to see your size across five sizing systems.
- Use Copy to save all results to your clipboard, or Reset to start over.
About this bra size calculator
The bra size calculator takes two tape-measure readings and converts them into bra sizes for five international sizing systems: US/Canada, UK, EU, France/Spain, and Australia.
The calculation follows the standard fitting method. First, your band measurement is rounded to the nearest even inch to give the band size. Then the bust measurement is subtracted from that even band size; each inch of difference corresponds to one cup step — 0 inches is AA, 1 inch is A, 2 inches is B, 3 inches is C, and so on. Once the US cup and band are known, the tool applies fixed offset tables to convert the band to EU and French numbering (EU bands run roughly 32–34 above the inch value; French bands run 52–54 above) and maps cup letters to the regional conventions used in the UK, EU, and Australia. This is an estimate for general information and is not a substitute for advice from a qualified clinician.
For example, a band measurement of 33 inches rounds up to 34, and a bust measurement of 37 inches gives a difference of 3 inches, which maps to a C cup. The result panel would show 34C (US), 34C (UK), 75C (EU), 95C (FR), and 34C (AU). This tool is useful for anyone shopping across international retailers or checking whether a current size is still the best fit.
FAQ
- How does the bra size calculator determine my cup size?
- It subtracts your rounded band size from your bust measurement. Each inch of difference moves up one cup step: 0 inches = AA, 1 = A, 2 = B, 3 = C, 4 = D, 5 = DD, 6 = DDD, and 7 = G.
- What formula does the tool use for the band size?
- Your under-bust measurement is rounded to the nearest even inch. If the rounded number is odd, one inch is added to reach the next even number. This even value becomes the band size used in US, UK, and Australian sizing.
- How accurate is this bra size calculator?
- The result is a starting estimate based on standard sizing conventions. Fit varies between brands and styles, so treat the output as a guide rather than a definitive size. A professional fitting can confirm the best size for your body.
- What happens if I enter a bust measurement smaller than my band measurement?
- The tool shows a validation error and will not calculate a result. The bust measurement must be larger than the band measurement because the difference between the two determines the cup size.
- Does this tool store my measurements?
- No. The bra size calculator runs entirely in your browser; your measurements are never sent to a server or saved between visits. Closing or refreshing the page clears all inputs.
- Is the bra size calculator free?
- Yes. It is completely free to use with no signup, no account, and no usage limit.