In the most basic terms, the number is your band size, the distance around your chest just under the breasts. Getting to that number around your chest is a little tricky, so we will skip that. For now we just want you to have a basic understanding of how bra sizes work, and the different breast sizes. The letters are the cup size. The cup size equates to how big around your boobs are, or how full they are.
One important thing to keep in mind is that not all cup sizes are the same. A “C cup” is not always a C cup. Cup size is proportional to band size — meaning it’s dependent on your band measurement.
Example of how bra sizes work
To understand how bra sizes work, you need to understand the relationship between the band size and cup size, which is proportional as we mentioned. In the example below: A “D” cup means the bust/cup size is 4 inches bigger than the underbust/band size. You move up one letter for every inch. So for 4 inches, you count up A, B C and finally D:
32 inch band size, 36 inch bust size = 32D
30 inch band size, 34 inch bust = 30D
Bra band sizes go in increments of 2 inches… So when measuring, round to the nearest even number to find your band size. If in doubt, round up. You can also try the size above and the size below. This covers the basics of how bra sizes work. From here you may want to see all the bra sizes in order, or one of our other blog posts bout bras.