Bra Size Calculator — Free Bra Size Finder & Measurement Tool

Bra Size Calculator, Bra Size Chart, Guide & How to Measure Bra Size (US, UK, EU & International)

Between 75% and 100% of women wear the wrong bra size at any given time — a range so wide it reflects not the rarity of the problem but the inconsistency of the measurement systems themselves. This bra size calculator addresses that at the root: it calculates your correct band and cup size from two measurements, then converts your result across US, UK, EU, France, Japan, India, Australia, and more — instantly. It also covers what no generic chart does: brand-specific fit guides for Jockey, Victoria's Secret, Wacoal, Triumph, Panache, Freya, and others, so your calculated size translates accurately to the brand you're actually buying from.

What Is a Bra Size Calculator, and Why Does It Matter?

A bra size calculator — also called a bra size finder, bra fitting calculator, bra size estimator, or bra size predictor — takes two body measurements and uses the mathematical relationship between them to determine the correct band and cup size for your body. Some tools call it a bra size generator because it produces a full set of international sizes from a single input. This free bra size calculator online maps that result across all major international sizing systems, because the same body is labelled differently depending on which country's convention a brand uses. Whether you need a US bra size calculator, a UK bra size calculator, an EU bra size calculator, or an India bra size calculator, the tool outputs all of them from a single measurement.

The stakes are higher than comfort. A peer-reviewed study published in Chiropractic & Osteopathy found that 80% of young women wore incorrectly sized bras — 70% too small and 10% too large. A separate British study examining women seeking reduction mammaplasty found that every single participant wore the wrong bra size, with the majority underestimating their back (band) measurement by an average of 4 inches and overestimating their cup size by an average of three sizes. Persistently wearing an ill-fitting bra has been associated with breast pain, back and shoulder pain, shoulder grooving from straps, poor posture, and skin irritation.

The root cause of widespread misfitting is not individual error — it's systemic. Between 75 and 100% of women wear the wrong bra regardless of breast size, and this is substantially driven by the lack of standardisation across brands and countries rather than simple consumer mistakes. Different brands use different fit models. Different countries use different band numbering conventions. The same label — "34D" — can represent genuinely different physical measurements at Victoria's Secret, Wacoal, and Panache. An accurate bra size calculator gives you the correct bra size as a starting point — both the size code and the underlying measurements — so you can always cross-reference against any brand's own chart rather than relying on a single label.

How to Calculate Bra Size from Bust & Band Measurements

The calculator operates on two simple mathematical relationships that underpin all bra sizing systems worldwide. Think of it as a bust measurement calculator and a band size calculator combined — the underbust gives the band, the overbust gives the cup. Understanding them removes the mystery from any conversion chart you encounter.

The Core Formula

All bra sizing ultimately comes down to two related measurements:

• Underbust (band circumference) — underbust measurement calculator: Measured snugly around the ribcage directly under the bust. This determines the band number in US/UK systems (rounded to the nearest even number).
• Overbust (bust circumference) — overbust measurement calculator: Measured loosely around the fullest part of the bust. The difference between this and the underbust determines the cup letter.

Band Size Calculation

The bra size formula calculator uses your underbust circumference in inches, rounded to the nearest even number, as your band size. Older US sizing guides instructed women to add 4 or 5 inches to the underbust measurement to arrive at band size — a practice that originated when bra fabrics had little stretch and needed the addition to allow comfort. Modern elastic fabrics make this unnecessary, and the +4/+5 method systematically produces bands that are too large, forcing cup downsizing and misfitting. The current standard — used by the UK bra fitting industry and most specialist lingerie retailers — is to use the underbust measurement directly as the band size.

Most women who've been wearing the wrong size for years were told to add 4 inches by a fitter or an old chart. It's not their fault — that method was standard for decades. It's just wrong now.

Cup Size Calculation

This is the core of any cup size calculator — your bra size by measurement comes down to a single subtraction. Cup size is the difference between your overbust (fullest bust circumference) and your raw underbust in inches:

• Less than 1 inch: AA cup
• 1 inch: A cup
• 2 inches: B cup
• 3 inches: C cup
• 4 inches: D cup
• 5 inches: DD cup (US) / DD cup (UK) — same letter, same volume
• 6 inches: DDD cup (US) / E cup (UK) — this is where US and UK diverge
• 7 inches: G cup (US) / F cup (UK)
• 8 inches: H cup (US) / FF cup (UK)

The US and UK systems are identical up to D cup. Above D, they use entirely different letters for the same physical size. This is the single most common source of international bra shopping errors — and it's entirely the fault of inconsistent labelling, not the shopper.

The Cup Volume Principle (Why Cup Letters Alone Mean Nothing)

A D cup on a 32 band holds significantly less volume than a D cup on a 38 band. The letter describes a proportion, not an absolute size. A 32D and a 38D are not the same physical size — they share only the same difference between band and bust. This is why the statement "I'm a D cup" is meaningless without a band number. It is also the entire mathematical basis of sister sizing: changing the band by one step while shifting the cup letter in the opposite direction maintains constant cup volume. A 34C, 32D, and 36B all hold identical amounts of breast tissue.

This is why "I'm a D cup" means almost nothing on its own. A 32D and a 38D are completely different bras. The letter only makes sense with the number.

Cup Size by Measurement Difference — Quick Reference

Bars represent relative cup volume increase per step. UK/India cup naming shown (DD, E, F, FF, G). US equivalents: UK DD = US DD; UK E = US DDD; UK F = US G; UK FF = US H.

International Bra Size Converter & Chart — US, UK, EU & India

This section works as a complete international bra size converter and bra size guide calculator — covering every major system including a US to UK bra size converter, UK to US bra size calculator, EU to US bra size converter, and India to US bra size converter. The same body has a different label in every country; the tables below map them all.

This bra size chart covers band conversions and cup naming across all major international systems. Band sizes are listed for a common underbust range. Cup letters are shown in the two most distinct systems — US and UK/India — with equivalences across EU, France/Belgium/Spain, Japan, and Australia.

Band Size Conversion Table

Note: EU band = underbust in cm rounded to the nearest 5 — no addition applied. French/Belgian/Spanish band = EU band + 15 exactly. Japanese bands follow EU conventions with cup letter listed first (e.g., C75 not 75C). Australian bands use dress-size numbers: AU 10 = US/UK 30, AU 12 = US/UK 32, AU 14 = US/UK 34. India uses US/UK band numbers exactly.

Cup Size Conversion Table — US vs UK/India vs EU vs Japan

Bold values indicate where US and UK cup naming diverge — the most common source of international sizing errors. Japanese cups run 1–2 sizes smaller than US/UK equivalents due to a different measuring methodology; the range shown reflects this variance.

Sister Sizes — Same Cup Volume, Different Band

Sister sizing is the most practical concept in bra fitting that most women never learn. It solves the most common bra fitting problem: the cup fits but the band doesn't — or the band is fine but the cup is slightly off.

The rule: for every band size you go up, drop one cup letter. For every band size you go down, go up one cup letter. Cup volume remains constant. Only band tension changes. Here's an example using a 34C as the reference size:

When to use sister sizing: if a bra fits in the cup but the band feels too tight even on the loosest hook, try the next band size up with one cup size down. If the band fits but the cup is slightly small, try the next band size down with one cup size up. Sister sizes are particularly useful when shopping across brands — a 34C in one brand may fit like a 32D in another due to manufacturing variation.

Sister sizing has a limit. Moving more than two band sizes from your correct fit shifts the band geometry enough that the wire placement, strap positioning, and cup angle no longer work correctly for your shape. Use it for one-step adjustments, not as a substitute for finding your correct band size.

Sister sizing is also useful when a brand runs small in the band — instead of returning, try the sister size. Same cup volume, different band number.

Cup Volume Equivalence Map — Sister Size & Bra Size Comparison Chart

Each diagonal of this table shares the same cup volume — this is the definitive bra size comparison chart for sister sizing. Cells highlighted in the same shade hold identical breast volume — only band size and cup letter differ. Use this to find your sister sizes across a wider range, or to cross-reference between systems that use different letters [6].

💡 Cells of the same shade share identical cup volume — they are sister sizes. Each diagonal (top-right to bottom-left) = one cup volume. Moving one column right and one row up keeps cup volume constant while increasing band size. This is why 34D, 36C, and 38B are all the same cup volume — the band changes; the cup content does not.

US, UK & EU Bra Size Calculator — Sizing Systems Explained

US Bra Size Calculator & Sizing

The US system uses inches for band measurements and a cup lettering convention that diverges from UK above D cup. US cup names above D are: DD, DDD (sometimes called F), G, H, I, J, K. There is no US E cup — the letter E is skipped. US brands using this convention include Victoria's Secret, Jockey (US), Calvin Klein, Maidenform, Bali, and Wacoal US. The band number in US sizing corresponds directly to the chest circumference in inches where the band sits. To use this as a US bra size converter, simply enter your measurements — the tool outputs your US size alongside all other systems.

UK & India Bra Size Calculator

UK bands use the same numbers as US (30, 32, 34, etc.). UK cups use a different sequence above D: DD, E, F, FF, G, GG, H, HH, J, JJ, K. There are no triple letters. FF comes after F, GG after G — a unique feature of the UK system that provides more precision at larger cup sizes. UK sizing is widely considered the most consistent system globally, particularly for larger cups, and is used by specialist brands like Panache, Freya, Fantasie, Curvy Kate, Elomi, and Bravissimo. India follows UK conventions exactly — an Indian 34D is a UK 34D, making this tool a direct India bra size calculator as well.

European (EU) Bra Size Calculator

EU band sizes are based directly on the underbust measurement in centimetres, rounded to the nearest 5. A US/UK 34 band (underbust approximately 32–33 inches / 81–84 cm) becomes EU 75. No addition is applied. EU cups use a simple alphabetical sequence — A, B, C, D, E, F, G, H — with no double letters (no DD or FF). EU sizing is used across Germany, Austria, Belgium, Netherlands, and most of Scandinavia. This tool functions as a complete European bra size calculator, converting your measurements to the EU standard automatically.

French, Belgian & Spanish Sizing

France, Belgium, and Spain use a variant of EU sizing where the band number is 15 higher than the EU equivalent. A US/UK 34 = EU 75 = French 90 (75 + 15 = 90). Cup letters follow EU conventions (simple alphabetical, no double letters). The same physical bra is labelled 75C in Germany and 90C in France. When shopping from French brands — Simone Pérèle, Chantelle, Passionata, Empreinte — always check which convention the brand uses, as some label in EU and some in the French convention.

Japanese Bra Sizing

Japan lists cup letter before band number — a B70 in Japan, not a 70B. Band numbers follow EU conventions: Japanese 70 = EU 70 = US/UK 32. The critical difference is in cups: Japanese cups run approximately 1–2 sizes smaller than their US/UK equivalents due to a different measurement methodology designed for the average Japanese breast shape. A US/UK 34C is approximately a Japanese 75D or 75E. When buying from Japanese brands (Wacoal Japan, Triumph Japan, Peach John, Amphi), size up at least one cup from your US or UK size.

Indian Bra Sizing

India follows UK bra sizing in band numbers and cup naming conventions. An Indian 34C is the same as a UK 34C — cup naming uses the UK sequence (D, DD, E, F, FF, G) not the US sequence (D, DD, DDD, G). Brands like Jockey India, Amante, Triumph India, Enamor, Clovia, and Zivame all use UK/India sizing. Manufacturing quality and cup construction vary significantly across Indian brands, meaning that even within the same size label, fit characteristics differ considerably.

Australian Bra Sizing

Australia uses UK cup naming (DD, E, F, FF, G, GG) but a different band numbering system based on dress size. Australian dress sizes run even numbers (8, 10, 12, 14, 16) and correspond to US/UK bra bands as follows: AU 10 = US/UK 30, AU 12 = US/UK 32, AU 14 = US/UK 34, AU 16 = US/UK 36. This band-as-dress-size convention can cause confusion, as an AU 14C and a US 34C are the same bra, but the 14 in Australia has nothing to do with inches.

Common Bra Fit Problems & Fixes — Signs of Wrong Bra Size

Most bra fitting problems come down to two root causes: the band is too large, or the cup is too small. The two often occur together because women who were told the wrong size by a fitter usually got a larger band and a smaller cup simultaneously. Use the table below as a bra fitting problems reference — each symptom points to a specific adjustment.

The most common wrong bra size pattern is a band 2–4 sizes too large paired with a cup 2–3 letters too small. This happens because the two measurements are linked — if the band is inflated by the old +4 method, the cup difference shrinks artificially. The calculator above uses raw underbust (not band) for cup calculation specifically to avoid this error.

Brand-Specific Bra Sizing Guide — Jockey, Victoria's Secret, Wacoal & More

Knowing your calculated size is the starting point. The ending point is knowing how a specific brand interprets that size — because a 34D at Victoria's Secret is not the same physical object as a 34D at Panache. This is not vague brand variation; it is documented, measurable, and often significant enough to require a completely different size within the same system.

For further brand-specific conversion needs, the UK Bra Size Calculator and the UK to US Bra Size Converter offer dedicated conversion tools for the specific UK↔US lookup. For Indian market brands, the Indian Bra Size Calculator applies UK/India conventions directly. For Japanese brands specifically, the Japan Bra Size Converter handles the cup size offset that most generic charts miss. For bikini top sizing from a bra size, the Bra Size to Bikini Size Converter applies sport-specific adjustments.