1940's Bra Sew-Along - Adjusting Bra Cups

It's time to talk about the bra cups! At this point you'll have chosen your size and sewn your muslin (don't worry, no deadline! I'm just posting this now per request). Some of you will find that the bra fits pretty well on the first try (lucky you!).

Here is how the pieces are meant to rest on your figure.

Others will find that they need more or less room in the cup area. That means we need to make adjustments to the seam between pieces A and B.

Above is the seam we're looking at highlighted in blue. For reference, the top of piece A should be about 7" from where a shoulder seam would sit on a t-shirt. The pattern doesn't use cups sizes, as we discussed earlier, but that doesn't mean we can't make cup adjustments. For our purposes, it's a good idea to only adjust cup size one size at a time. This pattern is approximately a B cup depth-wise, and the increase (or decrease) rate is 1/2" per cup.
Warning: adjusting the cups beyond a DD can really change the shape of the bra and it might not look the same after. I'm talking about uni-boob, a very real threat.

This is how you will need to add or subtract allowance from the seam:

Due to the shape of these pattern pieces, I recommend adding the brunt of your changes to the seam on piece B. First trace your pattern pieces onto a new sheet of paper (leave some room around them to make adjustments. To increase the cup size, add 3/8" to uppermost curve on piece B. Add 1/8" to piece A. This will equal 1/2" in total.

Note: If your girls tend to rest more to the side than front and center (some of us carry more fullness an inch or two nearer to the side), then you can shift the added bit to sit closer to your fullest point.

From this added bit, you'll want to smooth the new line to nothing until it blends to touch the side and center front seams at the ends, as illustrated above.
As you add this change, you want to make sure that the seam edges on the left of this diagram stay the same height. These still need to match up to piece D later on.

Now, by adding allowance to this seam, you're actually lengthening the seam line and piece B won't quite match piece A any more. This can be fixed by walking the pattern pieces together to match them up. Measure the difference between the pattern pieces and then add the difference to piece A as illustrated above in pink. If you make any changes to the sides of piece B, keep in mind that it still needs to match up with piece C.

Do the same to remove too much room at the cup seam by subtracting rather than adding the 1/2".

And just like that, you've adjusted your cups! Now it's time to test it again in muslin to see if that sucker fits better.

Happy sewing,