Most women wear the wrong bra size. Grab a tape measure, enter your underbust and bust below, and get your true US size plus UK/EU conversions and sister sizes.

Bra Size Calculator — Find Your True US Bra Size in 2 Steps | syedwaleed.com
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Bra Size Calculator — Find Your True US Size in 2 Steps

Enter two quick measurements and get your accurate US bra size instantly, plus UK and EU conversions and sister sizes that fit the same cup.

Your US bra size
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US
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UK
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EU
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Sister sizes — same cup volume, different band

If the band feels tight or loose but the cups fit well, try a sister size instead of changing your cup letter.

100% private

Your measurements never leave your browser. Nothing is uploaded, stored, or tracked.

No signup

No account, no email, no personal details — just enter two numbers and get your size.

Free forever

Full results, conversions, and sister sizes are free with no limits or paywalls.

How to use the bra size calculator

  1. 1Measure your underbust

    Wrap a soft tape measure snugly around your ribcage, directly under your bust. Breathe out normally and keep the tape level. Enter the number in step 1.

  2. 2Measure your bust

    Wrap the tape around the fullest part of your bust (usually across the nipples), keeping it level around your back. Do not pull tight. Enter the number in step 2.

  3. 3Get your size

    Hit “Calculate My Size” to see your US bra size instantly, with matching UK and EU sizes below it.

  4. 4Check sister sizes

    If the band feels too tight or too loose but the cups fit, a sister size gives you the same cup volume on a different band.

Why this calculator beats the rest

US, UK, and EU sizes in one place

Shopping an international brand? We convert your size across all three sizing systems automatically, including the tricky UK double-letter cups.

Sister sizes explained

Most calculators stop at one number. We show the sister sizes that hold the same cup volume, so you can adjust band fit without guessing.

Smart error checking

Impossible measurements — like a bust smaller than your underbust — get a clear, friendly explanation instead of a nonsense result.

Works in inches or centimeters

Toggle between imperial and metric units. The math converts precisely (1 inch = 2.54 cm) with no rounding traps.

Built for real bodies

We use the classic US fit method — band rounded up to the nearest even number, cup from the true difference — that matches how most US brands size their bras.

Private by design

Everything runs in your browser. Your measurements are never sent anywhere, because there is no server to send them to.

Bra size FAQs

How accurate is this bra size calculator?
It uses the classic US sizing method used by most American brands: your underbust rounds up to the nearest even band number, and your cup comes from the inch difference between bust and band. It is a strong starting point, but brands vary, so always try the size on when you can — and check the sister sizes if the band feels off.
Should I round my measurements up or down?
Enter your exact measurements — the calculator does the rounding. The band rounds up to the nearest even number (for example, a 32-inch underbust gives a 34 band), which is the standard US approach. Never add extra inches yourself; that is how people end up in the wrong size.
What are sister sizes?
Sister sizes share the same cup volume on different band sizes. Go up one band and down one cup (34C becomes 36B), or down one band and up one cup (34C becomes 32D). They are perfect when the cups fit but the band feels too tight or too loose.
Why is my calculated size different from what I usually wear?
Most people wear a band that is too big and a cup that is too small — it is the single most common fitting mistake. If your calculated size surprises you, trust the tape first: try the new size and compare how the band sits (level, snug, on the loosest hook) before deciding.
What is the difference between US, UK, and EU bra sizes?
US and UK sizes share band numbers but diverge on larger cups: a US DDD/F is a UK F, and beyond that the UK uses double letters like FF and GG. EU sizes use centimeters for the band (rounded to the nearest 5) with similar cup letters. This calculator converts all three for you automatically.
My bust measurement is smaller than my underbust — what does that mean?
That is physically impossible with correct measurements, so the tape was probably placed wrong on one of the two measurements. Re-measure your underbust snugly under the bust, then measure the fullest part of the bust without pulling tight. The bust number should be larger.
How often should I re-measure my bra size?
At least once a year, and after any big change: weight change, pregnancy, nursing, or a new fitness routine. Bodies shift, and an annual two-minute check keeps you out of a size you have outgrown.

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