DD Cup Bra Sizes DD-mystified

When is a DD cup bra not a DD cup bra? Well… all the time really!

The first thing to realise is that a “DD cup” doesn’t really mean anything without the band size paired with it. For example, a 30DD is not only smaller than a 38DD in the measurement around the band, but also in the capacity of the cup – there is no such thing as a “DD” size in itself.

This concept is best explained using the system of “sister sizes” – which you can find out more in depth in our guide to bra sister sizes. All of these bras are “DD” sizes for example – from 30DD to 38DD, each with a different band length and cup volume.

To find out the best size for you if you already have a bra that is fitting relatively well, our fitting guide has step by step instructions of what to look for in a well-fitting bra, and which steps to take to improve it. Starting at the beginning? How to measure bra size has you covered.

If you’d like to know why it’s so important to be sure which system you’re using to take your underband sizing, what makes DD+ brands different from “core size” ones, and understand more about DD+ as a size category in general  – this guide is for you!

What is the difference between DD+ sizes and A-D sizes?

Roughly speaking, once the difference between the measurement around your ribcage and the measurement around the fullest part of your bust is more than 5 inches, a DD+ size is likely to be a good fit for you. 

Bras designed for this size segment often use firmer underwires, more pattern pieces in the bra cups themselves, and sturdier fabrics and components, to provide more support and a more comfortable fit for a larger bust.

The difference in DD+ and below D band sizing systems, and why that matters

An important consideration if you’re already wearing a DD bra size of any kind and looking to shop for more, is what sizing system your current brand has been using. There are two different ways of sizing the band of bras (+4, and +0) and that can make a big difference as to which size you end up in. 

As DD+ sizes have risen in popularity, many bra companies making the “core” sizes of A-D cups have extended into DD cups as well. However, the core industry standard method of sizing bra bands (sometimes referred to as the “+4 method”) is not used by brands specialising in larger cup sizes, starting at DD and going up.

The +4 sizing method takes the measurement of around your ribcage, where your bra band sits, and adds 4 inches to it (and then rounds it up, if it’s an odd number). However DD+ specialists (like ourselves) will simply take the measurement as it is. For example, for a measurement of 30 inches, you may be used to wearing a 34 band bra using the +4 system. In DD+ specialist bras though, you would be wearing a 30 size band.

You can double check which system your current bras use by measuring yourself with a tape measure, or looking up their sizing guide online and seeing if they suggest adding 4 inches to the underband measurement. You can also get a rough idea by looking at the other sizes that brand makes – are they mostly below DD (so likely using +4) or above it?

Very importantly though, this will now mean your cup size totally changes as well. Our bra sister sizes guide covers this in more depth, but for quick reference you can use the chart below to find your new cup size if your band has changed. The golden rule is that every time your band size goes up, your cup size goes down, and vice versa.

If you’ve got any questions at all or would like to double check you’ve picked the right size, just drop us a note and we’ll be very happy to advise further.

30DD and 38DD bra sizes compared

Why choose a DD+ specialist bra if I can get one from brands carrying all sizes?

Well the great thing is, you can do either! If you find a bra you love and it’s in your size (don’t forget to double check whether the brand is using +4 or +0 band sizing) there’s so many more choices now than there used to be. Often brands starting at DD will incorporate more supportive features, or design aspects specifically for this segment - so if you've found yourself wanting a bit more secure fit, that might be a good option to explore. 

The important thing is finding a bra that makes you feel amazing every time you put it on.

Double D? Is that different to DD?

If you’ve been in a store and heard the fitter refer to a “double D” bra size, that’s what a “DD” size is – we just say “double” instead of repeating the letter when we describe the sizing out loud. The same applies to any other double lettering for different sizes, like FF (double F) or GG (double G). If you’re interested in which letters are double and which aren’t, bra sizes explained covers the whole list. 

Is D or DD cup bigger?

DD is one cup size larger than D. After the core cup sizes of A, B, C, D the alphabet continues as the sizes get larger, but with some sizes having double letters (such as DD or FF)

There’s no difference in the spacing between single and double letter sizes, a DD is one full size larger than D, just like E is one full size larger than DD.

What about DDD sizes?

DDD is most commonly used in the US, and converts to an E or F cup in UK sizes – one size up from DD.

Many larger cup bra brands use UK sizing, so it’s worth being familiar with how sizes convert. Our international size charts cover the differences at a glance. 

Is DD cup size big? Or small?

All bra sizes are relative, so while a 38DD is indeed a bigger cup volume than a 30DD, it’s important to remember this is just the level many brands start at.

For a long time, especially when larger sizes were hard to find, DD cups were sold as being the largest possible, fuelling the myth of “DD” as some kind of giant sizing.

In fact, not only is it extremely common to wear some version of a DD cup, it’s also very common to be mis-sized into one due to that being the largest available option to purchase from some stores. If you found yourself in a new band size after the +4 exercise above and wound up a 32F after thinking you were a 36DD, you’re not alone!

With bra cup sizing going up to L, LL, or M, DD definitely isn’t anywhere near the largest cup volume available, especially from specialist retailers.

The most vital thing to remember though? It doesn’t matter. Bra sizes exist purely for the purpose of being able to identify one that fits the way you want it to, gives you the level of support you would like, and feels comfortable.

Changing size to improve the fit you get from your bra doesn’t change anything else. As you can see from the wildly different cup letter you would get from using either +4 or +0 sizing, the very definition of “DD cup” completely depends on where you’re shopping in the first place!

So here's to a whole new world of bra size options opening up to you, and don't forget our expert fitters are on hand to help with any other sizing questions you may have.