Bra Size Conversion: UK, US, EU and AU

A bra size conversion works in two parts, because you convert the band number and the cup letter separately. UK and US bands use the same inch-based numbers, EU bands use centimeters, and Australian bands use their own scale. Cup letters match through D and then diverge between countries.

The tables below come from a published conversion chart and are an example chart. Brands cut bras differently, so check your brand's own chart before ordering. This is also why AI size recommendation for fashion stores works best when it matches a store's own sizes rather than a generic chart.

How do band sizes convert between UK, US, EU and AU?

The band number is the underbust measurement of the bra. US and UK use inches, Europe uses centimeters, and Australia numbers its bands differently.

This table is from the Size.ly bra size conversion chart, checked November 2026:

US / UK	EU	AU
28	60	6
30	65	8
32	70	10
34	75	12
36	80	14
38	85	16
40	90	18
42	95	20
44	100	22

The same source lists France and Spain on a band scale 15 above the European number. If you shop from a French or Spanish brand, read the label closely.

How do cup sizes convert?

Cup letters are the same in all four systems through D. After D, each country names its cups differently.

Using the same Size.ly chart (checked November 2026), the cups after D line up like this:

US	UK	EU	AU
DD / E	DD	E	DD
DDD / F	E	F	E
G	F	G	F
H	FF	H	G
I	G	I	H

Three patterns explain most of the confusion:

• The UK doubles letters. It goes E, F, FF, G, GG, so its letters fall behind European ones.
• The US uses both labels. Many US brands label DD as E and DDD as F, so the same cup can carry two names.
• Australia follows the UK, then runs one step behind. From DDD upward its letters lag the UK's.

Does the cup letter mean the same size at every band?

No. A cup letter describes the difference between bust and underbust, so the same letter holds a different volume on different bands. A 34D and a 38D have the same letter but are not the same cup size.

If you change band size, the matching cup also changes. This is called a sister size. Most brands publish sister sizes on their charts, so check the brand's own table instead of guessing.

How do you find your starting size?

Measure the band first. Wrap a soft tape measure snugly around your ribcage, just under the bust, and keep it level. Then measure around the fullest part of the bust.

The gap between the two measurements gives the cup. Because brands vary, treat the result as a starting point and try the size on or check the brand's chart.

How do you convert your size step by step?

Follow this worked method:

1. Find your current band and cup, such as 34D in US or UK sizes.
2. Look up the band in the table to get the EU or AU number.
3. Check the cup letter. If it is D or smaller, it stays the same.
4. If it is larger than D, use the cup table and confirm the brand's chart.
5. Compare the result with the brand's own size guide.

For example, a US 34DD becomes EU 75E and AU 12DD, according to the Size.ly chart. A UK 34DD becomes EU 75E and AU 12DD as well, since the UK and AU letters match at DD.

Why do conversions sometimes fail?

Brands vary in cut, fabric stretch and band firmness. Size.ly says in its notes that a brand's own size chart should override a general conversion.

Mixed labeling is another cause. The same item may show one size in the UK and another in the US.

The same issue appears across categories. Our guides to kids' clothing size conversion and men's suit size conversion cover how other garments are labeled.

What should store owners do about bra sizing?

If you sell bras or fitted tops online, put your own chart on every product page, with body measurements rather than only labels. List the countries you ship to and show the matching size for each.

A general conversion chart is a fallback, not a promise. A store's own size chart is more accurate, and a size scan can match a shopper's measurements against it. See how virtual try-on compares with size charts for when each one helps.

FAQs

Is a UK 34B the same as a US 34B?

Yes. UK and US band numbers match, and the B cup is the same in both systems. The letters diverge only after D.

What is the EU equivalent of a US 36C?

Using the Size.ly chart, a US 36C is an EU 80C. Check the brand's own chart, because brands differ in cut.

Why does my size change between brands?

Brands use different patterns, fabrics and fit models. A conversion chart gives a starting point, not a guarantee.

Should I trust a conversion chart or the brand's chart?

Trust the brand's chart. A general conversion is only a fallback when the brand gives no guidance.