Bra Size Calculator

Last updated: Jul 22, 2026 | Reviewed by Calkulator Team | 2 min read

Lifestyle

Find your correct bra size from two simple measurements

Over 80% of women wear the wrong bra size. Measure your underbust and bust circumference in centimetres, and this calculator converts them to US, UK, and EU sizes — plus sister sizes for alternative fits.

Get remeasured every year or after significant weight changes — bra size is not fixed for life.

Measurement Unit

Underbust (Band) Measurement

Measure snugly around your ribcage, just below the bust

Bust Measurement (fullest point)

Measure around the fullest part of your chest (loosely)

How to measure:
1. Underbust: tape measure snug around ribcage below bust
2. Bust: tape measure relaxed around fullest part
3. Measure in a well-fitting, non-padded bra

Your Bra Size

US Size

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UK Size

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EU Size

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Band Size —

Cup Size —

Measurement Difference —

Sister Sizes (same cup volume)

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Live Result Illustration

Visual summary — updates instantly as you enter values above

LIVE

Real-Life Guide to Using the Bra Size Calculator

Find your bra size from measurements. Use the examples and checks below to turn the number into a practical decision.

When this calculator is useful

Useful when buying bras online without trying them on first, after a weight change that likely shifted your size, or when you've never been professionally fitted and want a starting estimate before a store visit.

For most people, the best way to use the Bra Size Calculator is to try the real case first, then change one input at a time. That makes the trade-off visible. For example, with a loan calculator you can change tenure while keeping the same rate; with an investment calculator you can change return assumption while keeping the same monthly contribution; with a health, education or measurement calculator you can check how much one input changes the final category.

The result should answer a practical question: Can I afford this? How much should I save? Is this score enough? Is this measurement within range? What is the safer or cheaper option? If the output does not answer the decision clearly, adjust the inputs until the scenario matches your real situation.

Real-Life Example

Converting tape measurements to a size: A first-time buyer measures her underbust at 30 inches and her bust at 34 inches before ordering online.

1Underbust 30" rounds to a band size of 32; bust minus underbust = 34 − 30 = 4 inches, which corresponds to a D cup, giving a calculated size of 32D.

2Now change one input, such as rate, time, quantity, unit or score, and compare the new result with the first one.

The cup letter comes from the gap between bust and underbust, not from the bust measurement alone — two people with the same bust size can need completely different cup letters.

Practical Advice

Use the Bra Size Calculator as a planning tool, not just a number generator. Write down the inputs you used, because the final answer is meaningful only when you remember the assumptions behind it.

If the decision affects money, health, tax, safety, academics or legal compliance, keep a second check ready. That second check may be a bank quote, payslip, official rule, prescription, site measurement, mark sheet or invoice.

Common Mistakes

Measuring the band size over a padded or underwired bra instead of a soft, unpadded one, which adds bulk and inflates the band number by an inch or more.
Measuring the bust at the top of the chest instead of at the fullest part, usually across the nipple line, which understates the actual bust measurement.
Pulling the measuring tape too tight around the ribcage "for accuracy," which shrinks the band number and leads to buying a band that's too tight to wear comfortably all day.
Forgetting that cup size is relative to band size, not absolute — a 34C and a 36C have different actual cup volumes even though the letter is the same.
Assuming every brand fits identically — international brands (US, UK, EU) use different sizing conventions, so a calculated 34B may fit as a 75B or 15B depending on the label's regional system.

How to Interpret Results

The result gives a band size (from your underbust measurement, rounded to the nearest even number) plus a cup letter based on the difference between bust and underbust in inches — treat this as a fitting-room starting point, since brand cut and fabric stretch still cause real variation.

A good interpretation looks at both the main result and the supporting values. If a page shows totals, ratios, categories, schedules or warnings, read those together instead of focusing only on the biggest number.

Bra Size Calculator FAQs

Useful answers for interpreting the output, avoiding mistakes and using the result responsibly.

What two measurements does this calculator need, and how do I take them correctly?

It needs your underbust (measured snugly around your ribcage, directly under the bust) and your bust (measured around the fullest part, usually across the nipple line), both taken while wearing a non-padded, well-fitting bra or no bra at all. Keep the tape parallel to the floor and snug but not tight.

How is the cup letter actually determined?

It's based on the numeric difference between your bust and underbust measurements in inches — commonly, a 1-inch difference is an A cup, 2 inches is B, 3 inches is C, 4 inches is D, and so on. This is why cup letters alone are meaningless without the paired band size.

Why did the calculator give me a different size than what I currently wear?

Many people wear an incorrectly sized bra for years — often a band that's too large combined with a cup that's too small — because that's what felt familiar, not because it's actually correct. A calculated result that differs from your habit is common and worth trying in-store.

Does the calculator account for "sister sizes"?

Not directly — a sister size is an equivalent fit achieved by moving one band size and one cup size in opposite directions (e.g., 34C ≈ 36B), useful when your exact calculated size isn't in stock. You can manually apply this rule to the result if needed.

Why do US, UK, and EU sizes look different for what should be the same fit?

Band sizing conventions differ by region — UK and US band numbers are usually similar, but EU sizes use centimeter-based band numbers (e.g., a US 34 is roughly EU 75) and cup letter systems can also shift by one or two letters between regions.

Is a calculator result as accurate as a professional fitting?

No — a trained fitter accounts for breast shape, tissue distribution, and how a specific bra style sits on your body, none of which a two-measurement formula can capture. Use the calculator as a starting point for online shopping, then adjust based on how the actual bra feels.

What if my underbust measurement is an odd number?

Most calculators round to the nearest even number for the band size, since bras are typically manufactured in even sizes (32, 34, 36, etc.) rather than odd ones. If you measure 33 inches, expect a calculated band of 32 or 34 depending on the rounding rule used.

Should I re-measure after weight changes or pregnancy?

Yes — both band and cup size commonly shift after a weight change of even a few kilograms, pregnancy, or breastfeeding, so it's worth re-measuring every 6-12 months or after any noticeable body change rather than assuming your size is fixed for life.

Understanding Bra Sizes

Bra sizes consist of a band number (chest circumference) and a cup letter (difference between bust and band). Each inch of difference equals one cup size: 1"=A, 2"=B, 3"=C, 4"=D, 5"=DD. UK and US bands are the same; EU bands are in centimeters (~5 cm increments) with slightly different cup letters.

Sister sizes have the same cup volume but different band sizes. If a 34B fits the cup but the band is too tight, try 36A. If the band is right but cup too small, try 34C. Professional fitting is recommended for the most accurate result as bra sizing varies between brands.

Example

Underbust: 32", Bust: 36":

1Band size: 32 (round to even)

2Cup: 36-32 = 4" = D cup

✓ Size 32D (US) / 70D (EU)

Frequently Asked Questions

How do I measure myself accurately for a bra size?

Use a soft measuring tape. For band size: measure snugly around your ribcage just under your bust — round to the nearest even number. For cup size: measure around the fullest part of your chest without compressing. Subtract band from bust measurement; each inch equals one cup size (0 = AA, 1 = A, 2 = B, 3 = C, 4 = D).

What are sister sizes in bras?

Sister sizes are bras with the same cup volume but different band and cup letter combinations. A 34D is a sister size to 32DD and 36C — the cup volume is identical, just the band is different. If a 34D band feels too tight but the cups fit, try a 36C for a more comfortable band with the same cup capacity.

Why do bra sizes vary between brands and countries?

Sizing systems differ by region. UK and US use the same band measurements but slightly different cup progressions past D. EU uses band sizes ~8–10 cm smaller (EU 80 = UK/US 36). French and Italian brands add a further offset. Always refer to each brand's size chart and measure yourself rather than assuming your size carries over between brands.