Beginners’ Sewing Series Part 3 | Determining Your Garment Sewing Cup Size

Brand new to sewing? Start here. The Sew Busty Beginners’ Sewing Series will be your step-by-step guide to learning garment sewing. Each installment will build upon the last, getting progressively more advanced in skills and techniques. Catch up with the whole series here.

Ever seen A, B, C, D, etc. on a garment (top, dress, etc.) pattern and been confused as to what that means? Here’s a hint: It’s not referring to your bra size.

I know, I know. That sounds batty. These are the same letters we use for bras, and, after all, pattern designers call these “cup sizes.”


I’m a size 30J in bras. I wear a garment cup size of DD/E or F.

Why is this? Well, because they’re just different measurements. Bra sizes, when done correctly, are based on your underbust and full bust measurements, because a bra gets its support from your ribcage. Garments – dresses, tops, jumpsuits – don’t generally hug in at the underbust, and instead hang from your shoulders and high bust. Thus, for garments, we use your high bust and full bust measurements to determine your garment sewing cup size.

(Not sure how to measure yourself? Check here.)

Once you have these measurements, you’ll subtract your high bust from your full bust. This difference will tell you your garment pattern cup size, per this chart:

Full Bust – High Bust =Pattern Cup Size

For example, my full bust is 40.5″. My high bust is 35.5″. That gives me a 5″ difference between high and full bust, putting me at a DD/E garment pattern cup size.

Now, some designers use a slightly different system to determine your garment cup size. Charm Patterns and Cashmerette, for example, both use a slightly different system, in which their cup size G is more like a DD in most designers’ patterns. All of this is to say always check the size chart of the pattern you’re making.

6 thoughts on “Beginners’ Sewing Series Part 3 | Determining Your Garment Sewing Cup Size

  1. Thank you for the wonderful info. This will help with making a giant FBA. The difference for my upper bust and bust are 11.5 inches. Any tips or useful information is welcome.


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