G Cup Guide

If you’re already wearing a G cup bra size of some variety, maybe you already know quite a lot about what to look for in a well-fitting bra, but have noticed your size seems to be wildly different depending on where you’re shopping.

Perhaps you’ve been previously fitted into a smaller cup size, usually with a larger band, just because that’s the biggest bra the store carries – and now you’ve been recently fitted and ready to explore your new world of sizing! Or you just have the distinct feeling your current bra isn’t cutting it and want to find out more about different sizes to see if you can get a better fit.

We specialise in luxury bras for sizes 30-38 DD-G, so this size segment is what we know best, and we’re here to help you find the perfect size for you, and the perfect bra in that size!

What does "G cup" actually mean?

The first and most crucial thing to know is that there’s actually no such thing as a “G cup” as a fixed size. Every cup size only exists in conjunction with a band size, so the volume of a 30G bra will be very different to a 38G, despite both being “G cup”.

Our article about sister sizing explains this in much more detail, but in essence, if the letter stays the same then the volume of a bra also increases up or down with every corresponding band size. A 34G bra is both one cup and one band larger than a 32G, not just one band size. This is really helpful to know if you’re online shopping and want to exchange a bra, as it’s an easy mistake to think this will just be making the band larger, assuming that “G cup” is a fixed definition – unfortunately not!

All of these bras are actually a G cup. From top to bottom, you can see 30G, 32G, 34G, 36G and 38G. Though they increase in band sizes, you can also see the cups are also getting slightly larger each time.

G cup bras of different sizes stacked together for comparison 

Five different G cup bras compared - 30G, 32G, 34G, 36G and 38G

If you’d like to learn more about which sizes to switch for to change a larger or smaller cup, or a larger or smaller band, we have easy charts plus a handy step by step reference checker over on our sister sizing guide.

Measuring G cup size in inches

The best way to define a “G cup” is to use a tape measure to get the size around your ribcage, and then around the fullest point of your bust.

A G cup is roughly either 8 or 9 inches difference between your underbust and overbust measurements. We use UK sizing, and include a FF cup size, so we would say 9 inches. Other brands that skip the FF cup would say 8 inches. Which just proves that checking the brand’s sizing system before ordering is a good idea!

Measuring over and under bust measurements to find bra size

However, we would say there’s more to it than just inch measurements. Our guide to bra fitting covers a lot of points about how to find the best fitting bra for you, and also using your current best fitting bra as a starting point for finding a better size. Your breast shape, personal preference, and so much more affect your final size, so don’t worry about finding a predefined letter and number combination, and just focus on finding a garment that makes you feel your very best.

US G cup and UK G cup

Another very important thing to note is that a UK G cup is very different to a US G cup. Depending which brand you’re buying from, it can make up to two whole cup sizes difference.

Many brands for the DD+ cup size segment (which includes G cups, everything up to it and beyond it!) are UK based, and use UK sizing. It’s always a good idea to check the size chart before ordering if you’re shopping online, just to double check which system is being used, to avoid any mistakes. 

Our international size charts will give you a quick reference guide to compare as well.

Is G cup the same as DDDD?

Just to add even more confusion to the mix, some US sizing systems will also go straight from D to DD, then DDD, then DDDD – that’s a lot of D’s! If we take every alphabetical letter in order, without any double letters, a G would work out as DDDD.

However, once you get to this size you might be better off shopping with a specialist brand, most of which, even with the US system, will use alphabetical sizing instead.

Is a G cup large? Or small? Where does it fit with other sizes?

In the industry, a typical size break where patterns will be reworked hits around a G cup. A style may work with so-called “core” A-D sizes, then be adapted for DD-G, then again for GG+, if a brand covers this entire size range - which is actually very rare! Most brands will focus on their own segment, so their customers are receiving the very best fit and design for their size.

Especially if shopping on the high street or in mainstream stores, it’s easy to think that a G cup is the largest possible size – or indeed a DD cup, depending where you’re shopping! However, there are so many sizes beyond this, right up to L, LL or M. Nowadays, the DD-G cup segment sits at the middle of the range, and is incredibly common. Also, each cup letter only exists together with the band remember - so a 30G will be much smaller than a 38G.

30G and 38G size bras compared for size

A 30G and 38G bra compared for size - both the cup and the band are larger on the 38G

What is a GG cup? Is that a different size?

No, that’s not a typo – GG is just the next size up from G in UK sizing. Not all letters are double letters in bra sizes, but after DD there are several which are. A common pattern for double letters is as follows – 


Though our standard size range stops at G, we can make any of our designs in 30-36GG as part of our custom service, so just drop us a note if you’d like to order one of those.

In conclusion...

The most important thing to remember is that bra sizing exists as a way to help you find the best fitting garment for you, even if multiple systems are all used across the industry. Whether you wear a G cup in one brand and an I cup in another, or a DDDD, or any other size – the important thing is being able to recognise what works for you, and knowing what to look out for when shopping for new styles. 

Though a "G cup" might not equal a definite size in itself, by measuring your underbust and overbust difference, knowing what to look for in a well-fitting bra, and being able to identify which sizing system you're looking at, you should be well on your way to finding the perfect bra for you.

If you have any questions about sizing, or would like some help fine tuning which one to go for, you can read any of our fitting guides or just contact us and our expert fitters will be happy to help.

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