|ALL THESE BRAS ARE A 32F WITH DIFFERENT CUP DIMENSIONS|
I know many women can't find their bra size and this is usually because they haven't tried on their correct size in the right style of bra. One of the biggest differences in bra style is the shape of the cup. If you're a 32F, for example, the bras available in this size will all have approximately the same cup volume, however, the volume can be dispersed in different ways. Below is a picture of the same volume of silly-putty molded into a wide and a narrow breast shape (Bratabase has an amazing resource for understanding breast shape). You'll notice that the wide base volume is shallower than the narrow based volume which is why we need different cup shapes.
The width of your breasts (often referred to as the breast root) makes a difference to how your breast volume forms your breast shape. A 32F women with a narrow root will have breasts that project forward more as the volume is stacked up over a smaller base. She may also notice that her breasts are round at the top as well. This woman needs a bra that has a narrow base (a narrow cup width) and a full, forward cup. If your cup feels very empty at the sides of your cup but you're spilling at the top then you want to look for styles with narrower wires and forward fuller cups.
A 32F woman with a wide root will find her breasts are spread over a wider area and so don't project as far forward. She needs a bra that can accommodate the width of her breasts and the cup doesn't need to project as far forward because her volume is spread out more. If your bra is poking your breast tissue at the side and you're not quite filling the cup then look for bras with wider wires and shallower cups.
Related Vlog Post: Cup Shapes and Bra Fit
The third direction that's important to consider when figuring out your breast shape is how far up your body your breast tissue extends (without a bra on). Some women have breast tissue high up on their body near their collarbone and this forms part of their breast volume so they need a long cup that can accommodate this tissue. Women with high tissue often find that they don't have much forward projection and so they need styles that are long in the cup but shallow in depth. Many women are very flat through their upper chest across the breast bone (their breast tissue doesn't become obvious until farther down their chest - usually, level with their armpit). If you're flat through your breast bone you'll find you can wear a variety of styles.
If you've been trying on the same style of bra, or even the same brand of bra, and are still struggling to find your size I recommend trying a different style or brand bearing in mind this information about how your breast root can affect the shape of your breast and so you'll need a cup shape that's right for you. xx