Bra Size Calculator: US, UK, EU & AU/NZ Conversions
Find your bra size from band and bust measurements. Converts to US, UK, EU (EN 13402), FR/BE/ES, and AU/NZ. Sister sizes, fit tips, shape guide. Free bra size chart and calculator.
What This Calculator Does
This bra size calculator converts your band and bust measurements into bra sizes across five regional systems: US, UK, EU (EN 13402), FR/BE/ES, and AU/NZ. It also generates a sister-size grid—alternative band-and-cup combinations that hold the same cup volume—so you can find a fit even when your exact size is unavailable.
- Who it helps:Anyone shopping for bras who wants a reliable starting point before trying on in person. Useful for online shopping, where knowing your size across regional systems reduces returns.
- What it outputs:A bra size in each of the five regional systems, a sister-size table, and fit guidance notes.
- What it does NOT do:It cannot account for brand-specific fit variation, breast shape (full-on-top vs. full-on-bottom), or padding. Measurements give volume; the right style requires trying on. Use the calculated size as a starting point, not a guarantee.
How the Math Works
Bra sizing rests on a single subtraction: cup size equals bust circumference minus band circumference.
In US/UK sizing (inches), each inch of difference maps to one cup letter: 1″ = A, 2″ = B, 3″ = C, and so on through the alphabet. In EU sizing (EN 13402, centimeters), each 2 cm of difference equals one cup step. The band measurement is rounded to the nearest even number per industry standard.
- Sister sizes:Moving up one band and down one cup (e.g., 34C → 36B) preserves the same internal cup volume because the larger band compensates for the smaller cup designation. The reverse also works: 34C → 32D.
- Legacy sizing:Some traditional brands add 4–5 inches to the measured band before calculating the cup. This calculator uses modern fit standards, which generally provide better support. If a brand feels too tight, try the sister size up rather than switching to legacy math.
- Regional conversions:EU band is in centimeters (70, 75, 80…). FR/BE/ES adds 15 to the EU band (e.g., EU 75 → FR 90). AU/NZ uses a dress-size convention (e.g., US 34 ≈ AU 12). Cup letters diverge above D: UK uses DD, E, F, FF; US often uses DD, DDD, G.
How to Use This Calculator
Enter Your Measurements
- Band:Under-bust, snug, tape straight and parallel to the floor. We round to the nearest even number.
- Bust:Over the fullest part, tape parallel to the floor. Use inches or centimeters, toggle converts automatically.
Regional Size Differences
US vs UK cups
- UK double letters:UK uses DD, E, F, FF, G, GG where US often jumps to DDD, G. Same cup volume, different labels.
- EU band:EU band is in centimeters (70, 75, 80…). FR/BE/ES adds 15 to EU (e.g. EU 75 → FR 90).
- AU/NZ:Uses dress size convention for band (e.g. US 34 band ≈ AU 12).
Bra Size Calculator FAQ
How do I measure my band size?
Snug tape under your bust, straight across your back and parallel to the floor. Round to the nearest even number, industry standard. If you land on an odd number, try both the size above and below; band fit varies by brand.
How do I measure my bust size?
Over the fullest part (usually nipple level), tape parallel to the floor. Wear a non-padded bra or none. Keep the tape loose enough that it doesn't compress your chest.
Why is bust size larger than band size?
Bust wraps the fullest part of your chest; band sits under the breasts. The difference drives cup size. In inches: 1" = A, 2" = B, 3" = C. In cm (EN 13402): per cup. So in both systems.
What are sister sizes?
Same cup volume, different band. 34C, 36B, and 32D hold the same. Band too tight? Go up a band, down a cup. Cups gaping? Try down a band, up a cup.
Do sizes vary by brand?
Yes. Bra sizing isn't standardized. Use our calculator as a starting point, then try on in person. UK uses DD, E, F, FF where US often uses DD, DDD, G, our Global Sizes grid handles the conversion.
What does the AA cup fit tip mean?
When bust − band is under 1 inch, an AA may fit better. Many stores skip AA/AAA. Look for brands that carry smaller cups, or try bralettes and wireless styles.