How do bra sizes go? Demystifying the alphabet soup.

For many women, finding the perfect bra size can be a daunting task. With so many sizes and styles to choose from, it’s easy to get confused. In this article, we’ll take a closer look at how bra sizes work so you can make an informed decision when it comes to choosing the right bra.

The Anatomy of a Bra

Before we dive into bra sizes, let’s take a look at the different parts of a bra. Understanding the anatomy of a bra can help you better understand how it fits and supports your breasts.


The cups of a bra are the parts that hold your breasts. They can be made of various materials, including foam, padding, and lace. Cup size is determined by the difference between your bust measurement and your underbust measurement.


The straps of a bra are the parts that go over your shoulders. They can be adjustable or non-adjustable and can be made of various materials, including fabric, elastic, or silicone. The straps are responsible for providing additional support to the breasts.


The band of a bra is the part that goes around your ribcage. It provides the primary support for your breasts and should fit snugly around your body. The band can be made of elastic or non-elastic materials.

How Bra Sizes Work

Bra sizes are made up of two components: a number and a letter. The number represents the band size, and the letter represents the cup size. For example, a 34D bra would have a band size of 34 and a cup size of D.

Band Size

Band size is determined by measuring the circumference of your ribcage just below your breasts. If you measure an even number, that is your band size. If you measure an odd number, add 1 inch to determine your band size. For example, if your ribcage measures 33 inches, your band size would be 34.

Cup Size

Cup size is determined by measuring the fullest part of your breasts and subtracting your ribcage measurement from that number. The difference between the two measurements is used to determine cup size. The following chart shows how cup size is determined based on the difference between your bust and underbust measurements.

Difference (inches) Cup Size
0-1/2 AA
1/2-1 A
1-2 B
2-3 C
3-4 D
4-5 DD/E
5-6 DDD/F
6-7 G
7-8 GG/H
8-9 HH/I
9-10 J

Sister Sizes

It’s important to note that not all bra brands use the same sizing system. If you find that your usual size doesn’t fit quite right, try your sister size instead. Sister sizes are sizes that have the same cup volume but a different band size. For example, if your usual size is 34D, your sister sizes would be 36C and 32DD.

Choosing the Right Bra

Now that you understand how bra sizes work, it’s time to choose the right bra for you. Here are some things to keep in mind:

  • Make sure the band fits snugly around your ribcage. It should be firm but not too tight.
  • The cups should encase your breasts completely without any spillage over the top or sides.
  • Adjust the straps so they provide additional support without digging into your shoulders.
  • Try on different styles to find one that works best for your body type.

Frequently Asked Questions

Here are some commonly asked questions about bra sizes:

  • What is the most common bra size? The most common bra size is 34B.
  • Is it normal for my bra size to change over time? Yes, it is normal for your bra size to change due to weight fluctuations, pregnancy, and aging.
  • Do all brands use the same sizing system? No, not all brands use the same sizing system. Be sure to check the sizing chart for each brand before purchasing a bra.
  • Can one bra size fit all? No, different styles and brands may fit differently, so it’s important to try on different sizes and styles to find one that fits you best.


Choosing the right bra size can make all the difference in how you look and feel. By understanding how bra sizes work and trying on different styles, you can find the perfect bra for your body type. Don’t be afraid to ask for help from a professional if you need it!



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