Bra Size Conversion Explained: How to Order the Right US, UK, and European Cup Size Online

Shopping for bras online gives you access to more brands, styles, and sizes than any one store can stock, but bra size conversion is where most online orders go wrong. A 32DD is not the same cup volume as a 36DD. A UK G cup is not equivalent to a US G cup. And your size can change from one brand or style to the next.

Before ordering, it is important to consider the band, cup volume, sizing system, breast shape, and fit notes for the specific bra. Here is how Breakout Bras helps take the guesswork out of finding your bra size online.

The short version: a UK G cup is a US I cup, not a US G cup. European brands number their bands 65, 70, and 75 instead of 30, 32, and 34. And cup volume changes with the band, so a 32DD and a 36DD are not the same size. Use the international bra cup size conversion chart as your starting point, then read Melissa's Comments on the product page before you order.

Bra Cup Sizes Explained: Why Cup Size Changes With the Band

One of the most common bra sizing misconceptions is that every DD cup is the same size. In reality, cup size is relative to band size. As the band size increases, the cup volume also increases.

For example, a 32DD has a smaller cup volume than a 36DD, even though both bras use the same cup letter. That means your cup letter usually needs to change whenever your band size changes.

If the cups fit well but the band feels too tight, go up one band size and down one cup size. If the cups fit well but the band is too loose, go down one band size and up one cup size.

Using US sizing as an example:

• 30DDD/F
• 32DD
• 34D

These are sister sizes, meaning they hold approximately the same cup volume on different band sizes.

What Is Sister Sizing, and When Should You Use a Sister Size?

Sister sizing is the process of changing the band and cup together to maintain a similar cup volume:

• Go up one band size and down one cup size.
• Go down one band size and up one cup size.

For example, if you wear a 32DD but need a looser band, you might try a 34D. If you need a firmer band, you might try a 30DDD/F.

Sister sizing can be a useful troubleshooting tool, but it does not create an identical fit.

Changing the band size may also change:

• Wire width
• Cup depth and shape
• Center gore height
• Strap placement
• Band stretch and overall support

Because the band provides most of a bra’s support, moving too far away from your ideal band size can affect how securely the bra fits.

Breakout Bras carries a large selection of sizes, so we usually prefer to fit customers in their best band and cup combination instead of relying on a sister size for everyday bras.

However, sister sizing can be helpful in certain situations.

We may use sister sizing:

• For tankinis or one-piece swimsuits when additional body length is needed
• When a preferred color or limited-edition style is unavailable in the customer’s usual size
• After weight loss or weight gain when the band has changed but the customer’s cup volume appears similar
• As a starting point when determining a new size from a previously well-fitting bra

US vs. UK vs. European Bra Sizes: Why the Same Letter Means Different Things

Breakout Bras carries bras from the United States, United Kingdom, Poland, and other European countries. These brands do not all follow the same cup progression, which is why the letter printed on the tag does not tell the whole story.

A US G cup and a UK G cup are not equivalent. In many size ranges, a UK G cup is equivalent to a US I cup. Ordering only by the cup letter can result in receiving a bra several cup sizes smaller or larger than expected.

Before ordering an unfamiliar brand, check our international bra cup size conversion chart.

US Bra Sizing: Why DD, E, DDD, and F Overlap

Most US brands progress through the alphabet, although the sequence can vary between manufacturers. DD may also be labeled E, while DDD may be labeled F. Some brands continue with single letters, while others use additional D letters.

Because US sizing is not completely standardized, always check the individual brand and product information before ordering. 

UK Bra Sizing: The Double-Letter Cup Sequence

UK brands use double letters in much of their cup progression. A common UK cup sequence is:

D, DD, E, F, FF, G, GG, H, HH, J, JJ, K

UK sizing does not use an I cup. US and UK brands generally label their bands in inches, such as 32, 34, and 36.

Breakout Bras carries many UK brands because they tend to offer broad, consistent size ranges for smaller bands, fuller busts, and extended cup sizes.

European Bra Sizing: Band Numbers Like 65, 70, and 75

Most European sizing systems use single cup letters rather than double letters. Band sizes are commonly labeled with numbers such as 65, 70, 75, and 80 instead of 30, 32, 34, and 36.

These systems are not interchangeable based on the printed letter or number alone.

Always use a conversion chart and review the fit information for the individual brand.

Why Your Bra Measurements Are Only a Starting Point

Bra sizing is similar to sizing in other clothing. Two bras with the same size on the tag can fit very differently depending on the brand, fabric, construction, and cup shape.

Your measurements can help identify a starting size, but they cannot account for every factor that affects fit, including:

• Breast shape and fullness
• Breast tissue density
• Root width
• Projection
• Torso shape
• Differences between padded and unlined cups
• Firmness or stretch in the band
• The height and width of the underwire

You may need different sizes in different brands or even between two styles from the same brand. This does not mean that your measurements are wrong. It simply means that bra size is only one part of finding the right fit.

How to Check Your Bra Size Before You Order

Our website includes several tools to help you choose the best size and style before placing your order.

Read Melissa’s Comments

One of the most helpful resources on each product page is the Melissa’s Comments section. These fit notes explain how the specific bra fits compared with other styles.

Depending on the bra, Melissa’s Comments may tell you:

• Whether the band runs firm, loose, or true to size
• Whether the cups run large or small
• If we recommend ordering a different cup or band size
• Which breast shapes are most compatible with the style
• Whether the wires are narrow or wide
• How the fit compares with another popular bra

Always read these comments before selecting your size, especially when trying a new brand or ordering a Polish bra.

Check the US/UK Conversion Below the Size Menu

After selecting a size from the drop-down menu on a product page, look for the corresponding US or UK conversion displayed below it. This feature helps you confirm that you have selected the intended size before adding the bra to your cart.

For example, if you normally wear a UK 32G, the conversion should show the corresponding US size of 32I. If you select a size labeled only 32G US, you would be ordering a smaller cup.

Shop by Your Bra Size

You can also shop by bra size on the Breakout Bras website. Our size filters account for equivalent US and UK sizing so you can see available options across multiple brands without having to convert every size yourself.

Shop bras by size, brand, and style.

How to Order Comexim Bras: Polish Sizing Explained

Comexim is a popular Polish brand known for narrow wires, close-set cups, and distinctive padded and unlined styles. However, Comexim sizing and construction differ from many US and UK brands.

Comexim bras purchased directly from Poland typically use European band and cup sizing. At Breakout Bras, our Comexim bras are specially labeled using UK-based sizes because many of our customers are already familiar with UK sizing.

Even with our converted labels, customers need to order one to two cup sizes larger than their usual UK size in Comexim. The exact adjustment depends on the style, your breast shape, and your preferred coverage.

For example, a customer who normally wears a UK 32G may need a 32GG or 32H. This is a general starting point, not a universal rule.

Before ordering Comexim:

1. Start with your usual UK band size.
2. Review Melissa’s Comments on the product page.
3. Check whether that style runs small, shallow, or differently from other Comexim bras.
4. Contact our fitters if you are between sizes or new to the brand.

Because individual Comexim styles can fit differently, personalized guidance is often the easiest way to avoid ordering multiple sizes.

How to Order Nessa Bras

Nessa bras are also made in Poland, but their sizing is generally more standardized than Comexim sizing. You can typically determine your starting size using our international conversion chart.

As with any brand, we still recommend reading Melissa’s Comments because cup shape, wire width, and band firmness can vary by style.

How to Check the Fit When Your Bra Arrives

Once your bra arrives, try it on using the loosest set of hooks. A new bra should feel comfortably firm around the body so the band can provide support as the elastic relaxes with wear.

After putting it on, scoop and swoop all breast tissue into the cups and check the following:

• The band sits level across your back.
• The band feels secure without causing pain.
• The underwire surrounds your breast tissue without resting on it.
• The center gore sits comfortably against the chest when the style and breast shape allow.
• The cups do not wrinkle, gape, or cut into the breast tissue.
• The straps stay in place without carrying most of the weight.
• You can move, sit, and raise your arms without the bra shifting significantly.

If the bra does not fit as expected, the issue may be the size, the shape of the bra, or both. A different style may work better than simply changing the cup size.

Bra Size Conversion FAQs

Is a UK G cup the same as a US G cup?

No. A UK G cup is equivalent to a US I cup in most size ranges. UK sizing uses double letters such as DD, FF, GG, and HH, and it skips the I cup entirely, so the letters fall out of step with US sizing above a D cup. Check the conversion chart before ordering any UK brand.

What is the US size equivalent of a UK 32G?

A UK 32G is a US 32I. The band number stays the same, because US and UK brands both label bands in inches. Only the cup letter changes.

Are all DD cups the same size?

No. Cup volume is relative to the band, so a 32DD holds noticeably less volume than a 36DD even though both are labeled DD. When your band size changes, your cup letter usually needs to change with it.

What is sister sizing?

Sister sizing means moving up one band size and down one cup size, or down one band size and up one cup size, to keep roughly the same cup volume. A 30DDD/F, 32DD, and 34D are sister sizes. It is a useful troubleshooting tool, but it does not produce an identical fit.

What size should I order in Comexim?

Most customers need to order one to two cup sizes larger than their usual UK size. Breakout Bras labels Comexim bras in UK sizing, but the brand still runs small, and because each bra is hand-made there is some variation between pieces. Read Melissa's Comments on the product page or contact our fitters before you order.

Do European bra sizes convert to US sizes?

They do, but never by the printed letter or number alone. European brands use band numbers such as 65, 70, 75, and 80 in place of 30, 32, 34, and 36, and single cup letters instead of double letters. Use the conversion chart together with the brand's fit notes.

Get Personalized Bra Sizing Help

You do not have to navigate bra size conversions alone. Our experienced fitters can help you compare US, UK, European, and Polish sizes while recommending styles that suit your breast shape and fit preferences.

Book an online fitting for personalized help from wherever you live, or schedule an in-store fitting at our Greenville, South Carolina location.

If you have a question about a specific bra or Comexim size, email our customer service and sizing team at service@breakoutbras.com.

Still unsure which size to order? Book a fitting before you buy, and let our experienced team help you find the right starting size and style.