Bra Size Calculator & Converter
The Bra Size Calculator & Converter does two jobs in one: it works out your true size from your measurements — an accurate multi-measurement method or a quick estimate — and converts a size you already know between US, UK, EU, French and Australian sizing, with a full cross-country size chart.
Measure your size, or convert US, UK, EU, FR, AU.
How to use Bra Size Calculator & Converter
- Enter your under-bust and bust measurements and the calculator finds your band and cup
- Or switch to 'I know my size' to convert a size you already have
- Read your size matched across US, UK, EU, French, and Australian systems
About Bra Size Calculator & Converter
This bra size calculator does two jobs: it finds your true bra size from your measurements, and it works as a converter and size chart between the US, UK, EU, French and Australian systems. If you already know a size, pick the system and read it in every other one. If you don't, measure — two ways.
The Quick estimate needs just your under-bust and bust. The Most accurate method uses the six-measurement approach favoured by fitting communities: three under-bust readings (loose, snug, tight) set your band from the snug measurement, and three bust readings (standing, leaning, lying) capture how your tissue really sits, so the cup is measured across positions instead of a single guess. It shows a cup range when you fall between sizes, plus your sister sizes (same cup volume, different band) to try if the band feels off. Bands use the modern 'snug band' method — no adding four inches, which older calculators do and which leaves the band loose and the cup too small. Cup letters are matched by the true bust-minus-band difference so they stay consistent even above a D. Everything runs in your browser — nothing you enter is uploaded or stored.
Prefer a chart? Every size lines up across US, UK, EU, French and Australian systems, so it works as a bra size chart as well as a calculator.
Frequently asked questions
- Is this a bra size calculator or a converter?
- Both — it does two jobs in one tool, and you switch between them with the toggle at the top. Use the calculator if you don't know your size: enter your measurements and it works out your band and cup. Use the converter — 'I know my size' — if you already have a size on a label: pick your system and read the equivalent in US, UK, EU, French and Australian sizing, with a full cross-country size chart.
- How do I measure my bra size at home?
- You need two measurements with a soft tape, kept level. For the band, measure snugly around your ribcage directly under your bust; for the bust, measure around the fullest part. Enter both in the calculator (inches or centimetres) and it gives your band, cup and the equivalent in US, UK, EU, French and Australian sizes.
- How does the calculator work out my band and cup?
- Your band is your under-bust (ribcage) measurement rounded to the nearest even inch, or nearest 5 cm — the modern 'snug band' method, with no adding 4 inches. Older calculators added 4, which leaves the band too loose and can shrink the cup letter to almost nothing. Your cup is the difference between your bust and your ribcage: each inch is one cup, so 1 inch is an A, 2 a B, 3 a C, and so on. If you already know a size printed on a bra label, use the 'I know my size' converter instead — printed labels follow the older cross-country charts, so the two can differ. Brands vary, so treat the result as a starting point.
- Which method gives the most accurate bra size?
- The Most accurate method. Instead of one under-bust and one bust reading it uses three of each — loose, snug and tight under-bust for the band, and standing, leaning and lying bust for the cup — because breast tissue sits differently in each position. It's the six-measurement approach fitting communities rely on, and it catches the between-sizes cases a two-measurement calculator misses. Quick estimate is fine for a ballpark; switch to Most accurate for a real fit.
- How do I measure my bra size with the six-measurement method?
- With a soft tape, kept level. Under-bust: measure around your ribcage three ways — relaxed (loose), firm (snug) and as tight as you can while breathing (tight). Bust: measure around the fullest part in three positions — standing upright, leaning forward about 90 degrees, and lying on your back. Enter all six and the tool sets your band from the snug under-bust and your cup from the bust readings, then shows the result in US, UK, EU, French and Australian sizing.
- What are sister sizes?
- Sister sizes are bras with the same cup volume but a different band — going down a band adds a cup letter and going up a band drops one, so 30D, 28DD and 32C all hold a similar cup. If your calculated band feels too tight or too loose, its sister sizes are the first thing to try, and the accurate method lists yours automatically.
- What does it mean if I'm between two cup sizes, like 28E/F?
- It means your bust measurements landed between two cups — common when tissue is soft or projects differently standing versus leaning. Keep the band snug and, if in doubt, size to the larger cup so it fully contains the tissue; a too-small cup causes spillage while the band does the support. Trying both cups in a sister size is the quickest way to settle it.
- Is a US 34D the same as a UK 34D?
- Yes — up to and including a D cup the US and UK letters match. They only start to diverge above D, which is exactly where this converter keeps them aligned by measurement.
- Why do cup letters differ between countries above a D?
- Each system names larger cups differently: the US uses DD, DDD/F, G…, the UK uses DD, E, F, FF…, and the EU steps straight through D, E, F. This tool lines them up by the actual bust-minus-band measurement, so a US DDD/F becomes a UK E and an EU F. Charts vary a little for very large cups, so treat those as a close guide and check the brand's own size chart.
- How do EU and French band numbers work?
- The EU band is your under-bust in centimetres (a US 34 band is an EU 75), and the French band is the EU number plus 15 (so US 34 = EU 75 = FR 90).
- Are these conversions exact?
- Band sizes convert exactly. Cup fit still varies by brand and style, and many Asian brands run about a cup smaller, so when a label publishes its own size chart, trust that over any general converter.
- Does the tool store the sizes I enter?
- No. Everything runs in your browser and nothing you select is uploaded or saved.