Bra Fitting Basics

Bra fitting can cause anxiety for many reasons, but it is important to remember first and foremost that you are not defined by any measurement and you are not a size. You wear a size that may change from one brand to the next, and it may change from one month to the next (or throughout the month!).

A bra size comprises two dimensions: a band size and a cup size. We'll start with understanding band size.

Band Size

A band size at its most basic is the measurement of your underbust - your rib cage directly underneath your breasts where they meet your torso. In the United States, UK, and Canada band sizes are measured in inches and come in two inch increments. Obviously, humans don't come in even two inch circumferences, which is why bras have stretchy elastic bands. The band size indicates the stretched length of the bra's circumference. Therefore, if your snug band measurement is an odd number, most people will round up to the larger even number.

The band size is critical to a good fit because it provides 80-90% of the support of the bra. A band that is too loose is one of the most common fit issues we see. When a band is too loose, the weight of the breasts is transferred to the shoulder straps, creating strain on the upper back and neck, which can cause long-term damage.

A key indication that a band is too loose is riding up the wearer's back, which in turn has the effect of the breasts falling lower in the front. You will often also see deep grooves in the shoulders where the weight has been transferred.

On the opposite end, a band that is too tight can cause abrasions and discomfort. This is far less common, but important to be aware of. It is important to note that red marks on the body after taking off a bra are completely normal for a properly fitted bra. Any form-fitting garment that you wear (think socks, jeans, etc.) will leave some marks by their nature. Bras are no exception, and are often doing much more heavy lifting.

Cup Size

Cup sizes are probably the most misunderstood clothing size unit across all types of clothes. A cup size is a completely relative measurement, and as such, means absolutely nothing about the size of a breast on its own. It is only meaningful in relation to the band size.

Most people learn that A cups are small, B cups are average, C are big, D are very big, and DD are the biggest breasts that exist. This is patently false. There are 15 cup sizes commonly manufactured, and even more carried here at Wildflower. Additionally, being dependent on band size, each cup size can be bigger or smaller based on the band.

At its most basic, a cup size is the difference between the snug underbust and full bust measurements. Each inch difference indicates a cup size. So a 4 inch difference would be a D cup. A five inch difference would be a DD cup, a six inch difference would be an E cup, and so on. (Different countries have different "bra alphabets." We use UK sizing at Wildflower for a variety of reasons which can be found here.)

Cup sizes can be tricky to determine based exclusively on measurements because how a bra fits is also determined by breast shape, density, and projection, but it is important to understand where they come from.

Sister sizing

You may have heard of the term "sister sizing." This is basically the concept of keeping the cup volume the same when changing band sizes. Because the cup size is relative to the band size going up a band size also increases the volume of the cup. So, if you go from a 34D to a 36D, you are increasing the band and cup size by 1 increment. If you want to increase the band size but keep the cup size the same, you would go from a 34D to a 36C. This chart is incredibly useful to visualize sister sizing. The cup volume is equivalent across each row even though the cup is a different letter.