Bra Size Calculator | Find your size and convert it between countries

Work out your bra size from two measurements, then see it in US, UK, EU, French, Italian, Australian and Japanese sizing along with your sister sizes. Uses the modern fitting method and shows the older plus four result for comparison.


What would you like to do?
Find my size from measurements Convert a size I already know
Measure in
Snug, straight around, directly under the bust.
Loose, straight around, across the fullest part.
Clear

How to measure

Wear an unpadded bra or none at all, and keep the tape level all the way round. For the underbust, measure directly beneath the bust and pull the tape snug, firm enough that it does not slip. For the bust, measure across the fullest part with the tape resting loosely, without compressing anything. Stand upright and breathe out normally. The difference between the two numbers is what decides the cup.

Why two different answers exist

For decades shops told you to add four inches to your underbust to get the band size. That convention dates from when bras were made of much less stretchy fabric, and with modern materials it usually leaves the band too loose, which pushes the weight onto the straps. Professional fitters now generally use the underbust measurement as it is, rounded to the nearest even number. This calculator uses that modern method and shows the older one alongside it, so you can compare when a size chart clearly assumes the old convention.

Why cup letters do not match between countries

Above a D cup the lettering diverges. The UK inserts double letters, so its run goes D, DD, E, F, FF, G. The US mostly runs D, DD, DDD, then G, H, I, though brands disagree with each other. Continental Europe uses single letters straight through: D, E, F, G, H. This means a UK 34E and a US 34DDD are the same cup while a US 34E, where it exists at all, is not. Always convert rather than assuming the letter carries across.

Checking the fit

A calculator gives you a starting point, not a verdict. The band should sit level and horizontal around your back, not ride up, and should be snug on the loosest hook so there is room to tighten as it stretches. Most of the support comes from the band, not the straps. The cup should contain everything without gaping at the top or cutting in, and the centre panel should lie flat against the breastbone. If any of that is off, try the sister sizes above.

Worth knowing

  • Sizes vary noticeably between brands and even between styles from the same brand. Treat your calculated size as the one to try first.
  • Measure again after any significant change in weight, after pregnancy, or roughly once a year.
  • If the band rides up at the back, it is too loose, not too tight. Go down a band and up a cup.
  • A new bra should fit on the loosest hook. Bands stretch with wear, and the tighter hooks are there to compensate later.
  • Nothing you enter here is stored or sent anywhere. The calculation happens on our server and is discarded immediately.

Frequently asked questions

Take two measurements with a tape kept level. Underbust: directly beneath the bust, pulled snug. Bust: across the fullest part, resting loosely. Enter both above. The underbust rounded to the nearest even number gives the band, and the difference between the two, at roughly one inch per cup, gives the letter.

Generally no, not any more. The plus four rule comes from an era of much stiffer fabrics and with modern elastic it usually produces a band that is too loose to support anything. Fitters now use the underbust measurement as measured. This tool shows both results so you can compare, but the modern figure is the one to try first.

A different band and cup combination holding about the same cup volume. Going down one band size and up one cup letter, or up one band and down one cup, keeps the volume roughly constant. So 34C, 32D and 36B are sister sizes. They are the first thing to try when the cup fits but the band does not.

They match up to D, then diverge. UK runs D, DD, E, F, FF, G, GG; US runs D, DD, DDD, then single letters. A UK E is roughly a US DDD, and a UK F is roughly a US G. Because the letters look interchangeable but are not, converting matters most for anyone above a D cup.

The number is the band measured in centimetres, not inches, so 75 corresponds to a UK or US 34. The letter is the cup, running straight through the alphabet with no double letters. French, Spanish and Belgian sizes add 15 to the European number, so the same band appears as 90 there.

That is the classic sign of a band that is too loose, even though it can feel like the opposite. Go down a band size and up a cup to keep the volume the same, so 36C becomes 34D. The band carries most of the support, so getting it snug matters more than the cup letter.

There is no enforced standard, so each brand cuts to its own block, and styles differ within a brand too. Balconette, plunge and full cup shapes in the same nominal size can fit quite differently. Use your calculated size as the starting point and expect to move a sister size in either direction.

It applies the standard method precisely, but the method itself is an approximation, and how the tape was held matters as much as the arithmetic. Breast shape, not just volume, affects which style fits. Use the result to narrow down what to try on rather than as a final answer, and check the fit points listed above.

How do you work out your bra size?

Measure your underbust snugly and your bust loosely. The underbust rounded to the nearest even number is your band, and the difference between the two, about one inch per cup, is your letter. This tool does both, converts the result into US, UK, EU, French, Italian, Australian and Japanese sizing, and lists your sister sizes.