G cup Guide Expert Tips 2025

G cup guide, If you're currently wearing a G cup bra size, you may already have some idea of what a well-fitting bra should feel like. But if you’ve noticed your size seems to change wildly depending on the brand or store, you're not alone.

Maybe you've been fitted into a smaller cup with a larger band in the past—simply because that’s the largest size the store carried. Or perhaps you’ve just had a professional bra fitting and discovered your true size falls into the G cup range. Either way, understanding how bra sizing really works—especially at this cup level—is essential to finding your perfect fit.

At Olivia Paisley Intimates, we specialize in luxury bras in sizes 30–38 DD to G cup, so helping you understand and shop confidently within this size range is what we do best.

What does "G cup" actually mean?

One of the most important things to understand is that a G cup doesn’t exist in isolation. A G cup is always tied to a specific band size. That means a 30G bra has a significantly smaller cup volume than a 38G, even though they share the same letter.

This concept is known as sister sizing. For example:

• A 32G is one band and one cup size larger than a 30G.

• A 34G is larger than a 32G in both cup and band.

So, when shopping online or exchanging a bra, remember: a G cup is not a fixed size. It only makes sense when paired with the correct band measurement.

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.

Visualizing G Cup Sizes Across Band Widths

To show how cup volume increases with band size, compare these:

• 30G

• 32G

• 34G

• 36G

• 38G

Though all labeled "G cup," the cup size grows slightly larger with each increase in band size. That’s why trying the same cup letter in different bands can result in dramatically different fits.

 

Three different G cup bras compared - 30G, 32G 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.

How to Measure for a G Cup Bra

To find out if you’re truly a G cup, grab a measuring tape and follow this method:

Step 1: Measure your underbust

Wrap the tape firmly around your ribcage, directly under your breasts. This is your band size.

Step 2: Measure your bust

Measure around the fullest part of your breasts without squishing the tissue.

Step 3: Calculate the difference

Subtract the underbust measurement from the overbust. In UK sizing:

• 9 inches difference = G cup

• (Some brands skip FF, using 8 inches for G cup, which aligns more with US sizing.)

⚠️ Always check the brand’s size chart. A UK G cup is not the same as a US G cup!

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 under-bust and over-bust 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!

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 muchmore 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

This is a common area of confusion:

• UK sizing includes: D, DD, E, F, FF, G, GG, H...

• US sizing may go: D, DD, DDD (F), DDDD (G)...

In UK sizing, a G cup is larger than a US G cup by about two cup sizes. That’s why many women mistakenly order bras that are too small when switching systems.

If you’re shopping international brands or online, always verify whether the brand uses UK or US sizing.

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

Is G cup the same as DDDD?

In some US brands, DDDD is used as an alternative to G cup. But this isn’t universal—and gets confusing quickly. Once you’re in DD+ territory, it’s usually better to shop with specialty brands that clearly label sizes with letters (UK system) instead of repeating D’s.

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.

A 32G, 34G and 36G bra compared for size - both the cup and the band are larger on the 36G

Is a G Cup Considered Large?

That depends on the context. In many mainstream stores, G cup bras are among the largest they carry, leading many to assume it’s at the top of the size range. However, in the world of full-bust lingerie, G cup is a mid-range size.

Lingerie brands often group patterns as:

• Core sizes: A–D

• Full bust: DD–G

• Fuller bust and beyond: GG–M

So if you’re wearing a G cup bra size, you’re in good company—and far from being at the extreme end of the spectrum.

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

• Always get fitted or remeasured—especially after weight changes or pregnancy.

• Know your sister sizes: If a bra fits in the cup but the band is too tight, try going up a band and down a cup.

• Use a fit-first mindset: Your "ideal" size may vary across brands. Focus on what feels and fits best.

Not a typo! In UK sizing, GG is simply the size after G. The sequence looks like this:

AA, A, B, C, D, DD, E, F, FF, G, GG, H, HH, I, J, JJ, K, L, LL, M

At Olivia Paisley Intimates, our core range runs through G cup, but we also offer custom sizing up to 36GG. Just send us a message if you'd like to place a custom order.

 

AA	A	B	C	D	DD	E	F	FF	G
GG	H	HH	I	J	JJ	K	L	LL	M

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.

Final Thoughts: G Cup Bras Aren’t One-Size-Fits-All

The most important takeaway? Bra sizing is a tool, not a rigid system. Whether you're wearing a UK 32G, a US DDDD, or a custom GG cup, what matters most is how the bra fits your unique shape and supports your lifestyle.

If you're new to the G cup world or looking for a better-fitting bra, explore our luxury collection of bras designed specifically for DD–G cups. Need help choosing your size? Our expert fitters are just a message away.

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 recognize 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 over bust 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.