Bra Size Calculator
Find your true bra size in 10 seconds. Accurate band, cup and sister sizes for US, UK, EU, India, Japan and Australia — using the modern (no "+4 inches") method bra fitters recommend.
Snug under your breasts, parallel to floor.
Around fullest part, loose, no compression.
For most accurate results, measure in the morning wearing a non-padded bra. Sister sizes are alternates with the same cup volume — try both if the calculator size feels off.
What is a bra size calculator?
A bra size calculator measures your under-bust (band) and bust (cup) to determine your true bra size. The modern method, used here, divides the bust-minus-band difference into one-inch cup increments — giving an accurate band, cup letter, and two sister sizes. It is more reliable than the outdated "+4 inches" rule still used by some retailers.
How to Measure Your Bra Size
Two measurements with a soft tape — that's it. Wear a non-padded bra so the band sits flat, and stand naturally.
Measure under-bust
Wrap the tape firmly under your bust where the bra band would sit. Pull snug but not tight enough to leave a mark. Round to the nearest whole inch (or centimetre).
Measure bust
Wrap loosely around the fullest part of your bust, usually across the nipple line. Stand naturally, breathe out, do not compress. Round to the nearest whole inch.
Read your size
Enter both measurements into the calculator above. The result shows your band size, cup letter, and two sister-size alternatives — all in your chosen sizing system.
What Are Sister Sizes?
Sister sizes share the same cup volume on a different band. If the calculator's result feels slightly off, your sister size is almost always the fix — not a different cup letter.
| Smaller band | Calculator size | Larger band |
|---|---|---|
| 30B | 32A | 34AA |
| 30C | 32B | 34A |
| 30D | 32C | 34B |
| 30DD | 32D | 34C |
| 32C | 34B | 36A |
| 32D | 34C | 36B |
| 32DD | 34D | 36C |
| 34D | 36C | 38B |
| 34DD | 36D | 38C |
Rule: if your band feels tight → go SMALLER band, LARGER cup. If band rides up loose → go LARGER band, SMALLER cup. Sister-size tool →
Cup Size Chart with Visuals
Each cup grows by 1 inch (≈2.5 cm) of difference between bust and band. Your cup letter is the difference, not an absolute volume.
Difference (bust minus under-bust) shown in inches. Same cup letter on different bands = different volume.
Bra Size Conversion Chart
Same fit, six different labels. Use this table to convert between US, UK, European, Indian, Japanese and Australian sizing.
| 🇺🇸 US | 🇬🇧 UK | 🇪🇺 EU | 🇮🇳 IN | 🇯🇵 JP | 🇦🇺 AU |
|---|---|---|---|---|---|
| 30A | 30A | 65A | 30A | 65A | 8A |
| 30B | 30B | 65B | 30B | 65B | 8B |
| 32A | 32A | 70A | 32A | 70A | 10A |
| 32B | 32B | 70B | 32B | 70B | 10B |
| 32C | 32C | 70C | 32C | 70C | 10C |
| 32D | 32D | 70D | 32D | 70D | 10D |
| 32DD | 32DD | 70E | 32DD | 70E | 10DD |
| 34A | 34A | 75A | 34A | 75A | 12A |
| 34B | 34B | 75B | 34B | 75B | 12B |
| 34C | 34C | 75C | 34C | 75C | 12C |
| 34D | 34D | 75D | 34D | 75D | 12D |
| 34DD | 34DD | 75E | 34DD | 75E | 12DD |
| 36B | 36B | 80B | 36B | 80B | 14B |
| 36C | 36C | 80C | 36C | 80C | 14C |
| 36D | 36D | 80D | 36D | 80D | 14D |
| 36DD | 36DD | 80E | 36DD | 80E | 14DD |
| 38C | 38C | 85C | 38C | 85C | 16C |
| 38D | 38D | 85D | 38D | 85D | 16D |
| 40C | 40C | 90C | 40C | 90C | 18C |
| 40D | 40D | 90D | 40D | 90D | 18D |
Need a country not listed? Use the full size converter.
5 Common Bra Fit Problems (and Fixes)
Most fit problems are not a wrong size — they're a wrong sister size, wrong cup style, or wrong brand for your shape.
Band rides up the back
Cause: Band is too loose — the band, not the straps, supports the bra.
Fix: Sister-size DOWN: smaller band, larger cup (e.g. 36C → 34D).
Cup gapping at the top
Cause: Cup is too big OR breast shape doesn't match cup style (projected vs shallow).
Fix: Sister-size DOWN one cup, or try a more contoured cup style.
Underwire pokes or sits on tissue
Cause: Wire is too narrow for your root width, or the cup is too small.
Fix: Go up one cup size, or switch to a brand with wider wires (Freya, Panache).
Straps slipping off shoulders
Cause: Band too loose, OR shoulders are narrow / sloped.
Fix: Tighten band one hook smaller, sister-size down, or look for U-back / racer styles.
Quad-boob (cups overflow at top)
Cause: Cup is too small.
Fix: Sister-size UP: larger cup, smaller band (e.g. 34C → 34D).
Why most bra calculators give the wrong size
Many older calculators tell you to add 4 inches to your under-bust to get your band. This rule comes from the 1930s, when bra fabric had no stretch and bands needed extra slack to breathe.
Modern bras use elastic blends. Adding 4 inches to your measurement gives a band that's 2–4 sizes too loose — which then makes the cup spec wrong, makes the bra ride up, and pushes weight onto your shoulders.
The result: most women are wearing the wrong size. Studies estimate 70–80% of women wear ill-fitting bras, and the +4 method is a major cause. Our calculator uses your actual under-bust measurement — the method bra fitters and lingerie professionals use today.
Try the modern calculator →Find your size in any country.
Bra sizing varies dramatically by country. Pick your region for accurate conversion charts and locally-stocked brand sizing.
Every bra fits differently.
A push-up doesn't fit like a sports bra. Get type-specific sizing and shopping advice.
How major brands really fit
Same number on the label doesn't mean the same fit. Here's how the most-shopped brands run — based on their published charts and fitter consensus.
Detailed guides for every size.
From AA to K cup — what each size looks like, how it should fit, and which brands carry it.
Frequently asked questions
12 most-asked questions about bra sizing, measuring, and fit.
How do I measure my bra size accurately?
What does the "+" or "-" sister size mean?
Why does the same size feel different across brands?
Should I use the old "+4 inches" measuring method?
Is this calculator accurate for plus-size or D+ cups?
Can I measure myself, or do I need a fitter?
How often should I re-measure?
What if I'm between two band sizes?
Do bra sizes run the same in the US and UK?
Why is band size more important than cup size?
Is the bra size calculator free? Do I need to sign up?
What sizes do the calculator results cover?
Last updated: April 2026 · Reviewed by: the mybrafit editorial team · Method: Modern (no "+4") measuring, used by professional bra fitters worldwide.
We are an independent fit-resource site. We don't sell bras. Our goal is to help you find your true size, then point you to retailers and brand-specific charts that respect it.
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