Are Bra Cup Sizes Universal?

Woman measuring bra size
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Finding the right bra size can be a confusing activity. If you’ve ever bought bras from different brands and ended up with the wrong size, you’re not the only one. 

This might lead you to ask, are bra cup sizes universal?

Well, they aren’t. And that’s another thing that only us girls know something about. Bra cup sizes vary for different regions. A size 34F in the US isn’t the same as 34F in the UK and is totally different in Japan or France.

That’s why we came up with this explainer to help you understand how the bra size system works, specifically for the US and the UK. I’ll tell you about their similarities, differences, and how you can find the most accurate bra size for you.

Bra Cup Sizes Explained

Bras are measured in two ways, the bands and cups sizes. These make up the bra sizes you’re familiar with: 32A, 34B, and so on. 

The numbers represent the bra’s band size while the letters represent your cup size. 

Bras are measured this way so you can find ones that fit comfortably around your ribcage while supporting your breasts. 

Together, these measurements represent the difference between your band and bust size. This helps you determine what cup size you need. 

You can find the difference by subtracting your band size from your bust size.

The band and bust are always measured in inches and cup size volume in letters, as mentioned. But things aren’t always straightforward when it comes to cup sizes. 

Bra sizes can differ from country to country. You’ll also have to consider that your band size can change. This happens when you gain or lose weight but your breast volume remains the same.

So what do you do when this happens? This is where the concept of sister sizes comes in.

What are Bra Sister Sizes?

Sister sizes are the bra sizes that are the closest to your bra size. You look for sister sizes if your band or cup size has changed and the bra you’re using doesn’t fit that well anymore. 

So let’s say you lost weight and your band size has decreased but your cup size remains the same, you need to get a bra with a smaller band size but can still have room for your breasts.

The general rule is to go one up for band size and one down for cup size. So if you have a 32D bra and want to look for its sister size, you go for a 34C.

US Vs UK Bra Cup Sizes

If you’re taking a vacation in the UK and you find yourself needing a bra, you may end up getting the wrong size especially if you have a bigger bust. 

UK residents going to the US might encounter the same problem since US and UK bras have different measurements which can be confusing to the unaware.

When it comes to band size, US and UK bra makers follow the same measurements. So you won’t have a problem with that. However, you still need to consider the materials and cuts used by the different brands.

For example, some brands always use stretchable and soft fabric while some use a stiffer material and can feel tighter despite being the same size.

The difference is in the cup size and this is where it can get confusing. US bra makers don’t use double letters in their sizing charts but UK manufacturers do. So in the UK, you’ll see DD and FF sizes.

However, you may still encounter US brands using the UK sizing system, making it more confusing for us ladies. But brands usually have the size conversion on their tags. There you’ll find its equivalent size in other countries.

Bra Cup Size Chart (US Vs UK)

Here’s a chart that’ll give you a clearer picture of the US vs UK bra cup sizing system:

Band vs Bust Difference (inches)US Cup SizeUK Cup Size

So you can see right here how US brands go through the alphabet without using double letters, although you may find US makers that use DD instead of E or DDD for an F. But those are the only exceptions.

You’ll notice that a UK F cup is bigger than a US F cup. That’s why you’ve got to be careful in checking what size system it is before making a purchase.

Bra Cup Sizes Smallest To Biggest

You can already see from the table above that sizes start at AA and can go up to O. However, your favorite brands might not carry all sizes. 

Mainstream brands usually have bra sizes from A to DD so those of you with bigger breasts might have a difficult time looking for bras that fit.

Though you’ll find special retailers or niche brands that offer special sizes, you’ll just have to know where to look. 

How To Figure Out Your Correct Bra Size

Now that you know the difference between US and UK bra sizes, the next step is to find your correct bra size. Unfortunately, we can’t just go to the store and try on bras so the best way to get an accurate fit is to measure your vitals.

Remember when I told you that the number and letter represent the difference between your band and bust sizes? You’ll need those two measurements to find your correct bra size.

How To Measure Your Band Size

The band size measures your ribcage while the cup size measures your breasts’ volume. 

To know your band size, measure your ribcage just underneath your breasts. The fit should be snug so that the bra will hold its place on your body. 

Measuring it loosely won’t give you support while doing the opposite will make it too tight and uncomfortable.

Once you have your ribcage number, add 3 inches to it and the resulting number is your band size. So if your ribcage is 29 inches, add 3 which will give you a 32-inch band. You’ll use this to determine your cup size.

But bra band sizes always come in even numbers. So if your band size is an odd number, you’ll have to round up. So if you have a 30-inch band, add 3 and you get 35 inches. Round it up to 36 and that’s your band size.

How To Measure Your Bra Cup

First, measure your bust loosely at the fullest part. Subtract the band size and the difference is your cup size. Here’s an example using the band size above:

Bust size = 34 inches

Band size = 32 inches

Difference = 2 inches

Bust and band size difference (inches)






Corresponding cup sizeAAABCDDD/EDDD/F

With this example, you have a B cup and your bra size is 32B. You can use the table I provided in the previous section to check your cup size for US and UK conversions.

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