Bra Size Calculator: US, UK, EU, FR and AU Sizes
Find your bra size from under-bust and bust measurements in cm or inches. Band to the nearest even inch, cup by the inch difference, EU and FR by EN 13402, AU bands and sister sizes. Nothing is uploaded.
Enter your under-bust and bust measurements to see your bra size.
About the Bra Size Calculator
The Bra Size Calculator works out a bra size from two tape measurements: a snug under-bust measurement taken around the ribcage just below the breasts, and a loose bust measurement taken around the fullest part. You can type them in centimetres or inches. The calculator shows the size in the US, UK, European (EU), French (FR) and Australian and New Zealand (AU) systems, the band and cup differences it used, the band the older "+4" method would give, and the two sister sizes that hold the same cup volume on a tighter or looser band.
This is a fitting guide, not medical advice. Bra sizes are not standardised between brands, so treat the result as a starting point and check the fit in the fitting room.
How to measure
Steps
- Wear a non-padded bra, or none, and stand straight with your arms relaxed.
- Under-bust: pull the tape snugly around your ribcage, directly under the breasts, keeping it level all the way round. Breathe out and read the measurement.
- Bust: wrap the tape loosely around the fullest part of the bust, level across the back, without squeezing.
- Enter both numbers and read your size in each system.
Band
The modern method used by most UK brands and fitters takes the under-bust in inches and rounds it to the nearest even number, so an under-bust of 30.6 inches gives a 30 band and 31 inches gives a 32 band. The older method, still printed on some US charts, added 4 inches to an even under-bust and 5 to an odd one. It was designed for rigid fabrics and usually gives a band that is too loose, so it is shown here for comparison only.
Cup
In the US and UK every inch of difference between the bust and the band adds one cup: under 1 inch is AA, 1 inch is A, 2 is B, 3 is C and 4 is D. After D the letters split. US brands go on with DD (also sold as E), DDD (F), DDDD (G), then H and I. UK brands use DD, E, F, FF, G, GG, H, HH and J. Australian brands follow the UK letters up to DD and then single letters: E, F, G, H.
European and French sizes
European sizes follow the EN 13402 approach. The band is the under-bust in centimetres rounded to the nearest 5 cm, so 75 cm is a 75 band. The cup comes from the difference between the bust and the under-bust in 2 cm steps: AA is 10 to 12 cm, A is 12 to 14 cm, B is 14 to 16 cm, and so on up to H at 26 to 28 cm. French bands add 15 to the European band, so EU 75 is FR 90. Because the European cup starts at 10 cm while UK and US cups start near zero and grow by a full inch, the letters do not line up from one system to the next. When the difference is under 10 cm the page says the cup is below AA on the European chart. Australian bands are labelled like dress sizes: the band-equivalence table used here puts AU 14 beside UK 32 and EU 80, so the AU band is the UK band minus 18.
Sister sizes
A sister size keeps the same cup volume on a different band. Going down one band size means going up one cup letter, and going up one band means going down one cup. If 30E fits in the cups but the band rides up, try 32DD; if the band is loose but the cups fit, try 28F.
Worked example
An under-bust of 75 cm (29.5 inches) rounds to a 30 band. A bust of 92 cm (36.2 inches) is 6 inches more than the band, which is a UK E and a US DDD/F. On the European chart 92 minus 75 is 17 cm, a C cup on a 75 band. The sizes are UK 30E, US 30DDD/F, EU 75C, FR 90C and AU 12E.
Privacy
Nothing is uploaded; every calculation runs in your browser and your measurements never leave your device.
Related tools
Convert centimetres and inches with the Length Converter, find your shape from bust, waist and hip with the Body Type Calculator, or check your weight for your height with the BMI Calculator.
Sources
- "Bra size", Wikipedia: band measurement methods, the HerRoom cup cross-reference table for US, UK and Australian cups, the EN 13402 European cup table and the international band-equivalence table.
- CEN. EN 13402 Size designation of clothes, European Committee for Standardization, 2001 to 2006.
Open-source credits
The calculations are implemented in-house in TypeScript, with no third-party library. They follow the published rules listed above: the nearest-even-inch band, one cup per inch for US, UK and AU, and the EN 13402 5 cm band and 2 cm cup steps for EU and FR.
Frequently asked questions
Why does the calculator not add 4 inches to my band?
The +4 method dates from rigid, non-stretch bras and usually gives a band that is too loose, so most of the support then falls on the straps. Modern UK brands and fitters round the snug under-bust to the nearest even inch instead. The page still shows the +4 band so you can compare it with an older chart.
Why are the US and UK cup letters different?
Both add one cup per inch and agree up to D. After that US brands use DD (or E), DDD (or F) and DDDD (or G), while UK brands use DD, E, F, FF, G and GG. A UK FF is therefore a US H. Always read a brand's chart in the system it is sold in.
Why do the European cup letters not match the UK letters?
European sizes follow EN 13402, which measures the cup as bust minus under-bust in 2 cm steps starting at 10 cm for AA. UK and US cups start near zero and grow by an inch, which is 2.54 cm, so the two scales drift apart. Many brands sell UK sizes in Europe, so check which system a label uses.
What is a sister size?
A sister size holds the same cup volume on a different band: one band size down and one cup up, or one band up and one cup down. If 32D fits in the cups but the band is loose, 30DD is the size to try.
Is my measured size the size I should buy?
It is a starting point. Bra sizes are not standardised between brands, and breast shape matters as much as volume. The band should sit level and snug on the loosest hook, the centre should lie flat against the breastbone, and the cups should neither gap nor spill. This is a fitting guide, not medical advice.