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Bra Size Converter

Converts bra sizes between UK, US, EU, France, Italy, Australia and Japan, or works the size out from underbust and bust measurements in centimetres.

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In short A bra size is two independent things and only one of them converts cleanly. The band is arithmetic: EU = UK × 2.5 − 10, so a UK 34 is a European 75, a French 90, an Italian 3 and an Australian 12, and that reproduces every published row from 28 to 46 without exception. The cup is a count, not a letter — it is how many inches bigger your bust is than your band — and what changes between countries is only the letter printed for that count. Five inches is a UK DD, a US DD and a European E. Seven inches is a UK F, a US G and a European G. The doubled letters are a British habit: the UK runs D, DD, E, F, FF, G, GG while Europe just continues down the alphabet, which is why the two columns fall out of step after D and never recover. Above DDD the American column stops being reliable at all, because US brands use E, F, G and DDD interchangeably for the same cup — so if you have a choice, take the UK or European size from a chart and treat the US one as a guess. If you are measuring rather than converting: measure snugly under the bust and round to the nearest even inch for the band, then measure across the fullest part and count the inches of difference for the cup. The old rule that told you to add four or five inches to the underbust is a hangover from unstretchy fabric, and following it is the single most common reason people wear a band several sizes too loose with a cup several sizes too small.

How to use the Bra Size Converter

  1. Choose whether you know a size or have measurements.
  2. Enter the band and cup, or the underbust and bust in centimetres.
  3. Read the equivalent in seven systems, with the cup difference in inches beside them.

About the Bra Size Converter

A bra size converter that separates the band, which is arithmetic, from the cup, which is a letter convention that differs by country — and says plainly where the American column stops being trustworthy.

What people use it for

  • Buying from a British, European or Australian shop when you know your size at home.
  • Working out a starting size from a tape measure.
  • Understanding why the same bra is a 34DD in one country and a 75E in another.

Details

BandEU = UK × 2.5 − 10. A UK 34 is a EU 75
FranceEU + 15, so a UK 34 is a French 90
Italy(UK − 28) ÷ 2, so a UK 34 is an Italian 3
AustraliaUK − 22, so a UK 34 is an Australian 12
CupThe inches between bust and band. Only the letter differs by country
UK doubles lettersD, DD, E, F, FF, G, GG — Europe runs straight down the alphabet
Sister sizesDown a band and up a cup keeps the same cup volume
PrivacyThe arithmetic runs in your browser. Nothing you type is sent anywhere

The maths behind it

This tool uses band EU = UK × 2.5 − 10, France = EU + 15, Italy = (UK − 28) ÷ 2, Australia = UK − 22. The cup is the difference between bust and band in inches; only the letter printed for that difference changes between countries. Every intermediate value is shown on screen, so the result can be checked by hand.

The band is arithmetic and reproduces every published row. The cup is a letter convention, and above DDD the American one is genuinely inconsistent between brands — the page says so rather than printing a number it cannot stand behind.

Where this tool stops

It converts nominal sizes and gives a starting size from measurements. It cannot account for cup shape, wire width, or brands that cut deliberately small, and it does not cover maternity, sports or bralette sizing, which use their own ladders.

Frequently asked questions

What is 34DD in European sizes?
A European 75E. The band converts by arithmetic — 34 × 2.5 − 10 = 75 — and the cup is five inches of difference, which the UK writes as DD and Europe writes as E. In France the same bra is a 90E and in Italy a 3E.
Why does the UK have DD, FF and GG?
Historical habit. British sizing inserts a doubled letter every second step above D, while European sizing simply carries on through the alphabet. The physical cup is identical; the two columns just fall out of step after D, which is why a UK F is a European G rather than a European F.
Should I add four inches to my underbust?
No. The plus-four rule dates from before elastic and is why so many people wear a band that rides up with a cup that overflows. Measure snugly under the bust, round to the nearest even inch, and use that as the band. If it feels tight standing still it is probably right — the band does most of the work.
Why is the US column unreliable above DDD?
Because American brands never agreed on what comes next. Some go DDD, some go E, some go F, and some use all three across different lines in the same catalogue. The UK and European ladders are consistent, so where a chart offers you a choice, take one of those.
What is a sister size?
A different band and cup that give the same cup volume — go down one band and up one cup, or up one band and down one cup. A 34D and a 32DD hold roughly the same amount; they differ in how tightly the band sits. It is the first thing to try when the cup fits and the band does not.
Does the Bra Size Converter cost anything?
There is no cost and no cap. The Bra Size Converter is not a demo of a paid product, so nothing is held back or watermarked.
Is what I paste into the Bra Size Converter stored?
No. The Bra Size Converter runs entirely in your browser using JavaScript. Because the work happens locally, the page also keeps working if your connection drops, and closing the tab is all it takes to discard everything.
What formula does the Bra Size Converter use?
It uses band EU = UK × 2.5 − 10, France = EU + 15, Italy = (UK − 28) ÷ 2, Australia = UK − 22. The cup is the difference between bust and band in inches; only the letter printed for that difference changes between countries. The full working is printed under the result, so you can follow every step rather than trusting a black box.
Who is the Bra Size Converter for?
Typical uses: buying from a British, European or Australian shop when you know your size at home. Working out a starting size from a tape measure. Understanding why the same bra is a 34DD in one country and a 75E in another. It is built for exactly those cases rather than being a general-purpose tool with this bolted on.
Is there anything the Bra Size Converter cannot do?
It converts nominal sizes and gives a starting size from measurements. It cannot account for cup shape, wire width, or brands that cut deliberately small, and it does not cover maternity, sports or bralette sizing, which use their own ladders. Knowing where a tool stops being trustworthy matters more than the cases where it works.
What figures does the Bra Size Converter work from?
Band is EU = UK × 2.5 − 10. A UK 34 is a EU 75. France is EU + 15, so a UK 34 is a French 90. Italy is (UK − 28) ÷ 2, so a UK 34 is an Italian 3. These are printed on the page itself, so you do not have to take them on trust.
Can I rely on this for exact work?
The calculation runs in double precision and the result is shown to ten significant figures, so converting a value and converting it back returns the original. What is displayed is rounded for readability; what is copied is not.

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