Today we are going to talk bust adjustments for the Quinn vest and Dress sewing pattern. Keep in mind that a princess seamed garment is one of the most intuitive patterns to make an adjustment on because you have so many seams to work with and no darts. My favorite way to make adjustments on this kind of pattern is sewing and fitting in real time. This works especially well if the adjustment is an inch or less. The pattern has 1/2" seam allowances so you can let out or take in along the seams after sewing if needed. That being said, a flat bust adjustment like I am going to show you used math and can be very helpful, so lets get started.
What is a Bust Adjustment
Our patterns are drafted for a C-cup (0-18 size range) or a D-cup (14-32 size range). These are sewing cup sizes and not ready-to-wear cup sizes. This is very important. A sewing cup size refers to the difference between your upper bust and full bust and not your bra size. The Quinn has both of these measurements on its size chart so it should be pretty clear to figure out if a bust adjustment is a good option for you. To figure out your sewing cup size, subtract your high bust from your full bust, and use the difference to compare to the following chart.
- 1″ = A cup.
- 2″ = B cup.
- 3″ = C cup.
- 4″ = D cup.
- 5″ = DD cup.
- 6″ = DDD cup
If your bust difference is more than the cup your size range is drafted for, you may want to do a Full Bust Adjustment. So for instance, if my upper bust is 29" and my full bust is 33", that is a difference of 4" or a sewing D cup. Since the 0-18 size range is drafted for a 3" difference, I would choose the size that corresponds with my upper bust measurement of 29" which is a size 0, and then do a 1" (0.5" each side) full bust adjustment to the size 0 bodice to get me a full bust of 33".
Conversely, if your bust difference is less than the cup your size range is drafted for you may want to do a Small Bust Adjustment. So for instance, if my upper bust is 29" and my full bust is 31", that is a difference of 2" or a sewing B cup. Since the 0-18 size range is drafted for a 3" difference, I would choose the size that corresponds with my upper bust measurement of 29" which is a size 0, and then do a 1" (0.5" each side) small bust adjustment to the size 0 bodice to get me a full bust of 31".
I will be showing you how to do both of these below.
Full Bust Adjustment
For this adjustment I am going to be adding a one inch adjustment to size 6 of the pattern. Because I work with half of the pattern, I will be adding 1/2" to the pattern piece. You will not need to make adjustments to any of the back pattern pieces. You will need pattern pieces 3, 4, and 5. I will be doing View A (cropped vest), but the tutorial works for all views of the pattern.
Because the apex for this pattern is just inside pattern piece 4, line up and mark the apex height on pattern piece 3.
Also, mark the 1/2" seam allowance on pattern piece 3 as shown below.
Next, draw 3 lines.
A is parallel with the grainline along the width of the pattern piece and ending at the apex.
B is straight down from the top corner to the apex.
C is from the apex to the bottom
Cut along A, ending at the apex, but leaving a small hinge. Cut along B and C, stopping at the seam allowance at the top and cutting in from the other side, leaving a small hinge at the stitch line.
Tape the bottom left section to a piece of paper. Open the right side so the C line is split by the amount you are adding (for me it is 1/2").
The right side is now shorter than the left. Cut along the lengthen shorten line to extend the right side so the bottom hem lines up. Tape paper behind as needed.
Trim off extra paper. Cut along line A, cutting straight though the seam allowance.
Close up the dart along line A. This will create a wedge at the right side seam line.
Tape paper behind it and measure the opening. Mine was about 1/4".
Get pattern piece 4. Add a line at the apex. Cut and split it the amount of the wedge you just measured (1/4" for me).
You also need to cut and split along the lengthen / shorten line the amount you added there (1/2" for me)
Make the same adjustments you did to pattern piece 4 to pattern piece 5.
And that is it for the full bust adjustment. One thing to keep in mind is that you added a bit of width to the side front panel for the waist and hips. I find it easiest to leave it as is for now and address that when sewing and fitting, but you can shave some width off at the waist and hips now if you choose.
Small Bust Adjustment
Now for a small bust adjustment. I do think that the small bust adjustment is much easier than the full one as it's simply taking a bit of width and length out of the pattern.
For this adjustment I am going to be taking a one inch adjustment out of the size 6 of the pattern. Because I work with half of the pattern, I will be subtracting 1/2" to the pattern piece. You will not need to make adjustments to any of the back pattern pieces. You will need pattern pieces 3, 4, and 5. I will be doing View A (cropped vest), but the tutorial works for all views of the pattern.
First, mark the 1/2" seam allowance as shown below.
Because the apex for this pattern is just inside pattern piece 4, line up and mark the apex height on pattern piece 3. Also mark in how much you are subtracting from the pattern piece. So for me, I am making a mark 1/2" in at the apex height.
Draw a new cutline, starting at the original, intersecting with the dot you just made, and ending around the waistline marking.
Cut along the new cut line and transfer notches.
Mark the new stitchline at 1/2" seam allowance. Measure the stitchline between the notches.
Mark and measure the stitchline on pattern piece 4 between the notches. Compare. The measurement for piece 3 will now be less than piece 4. 
Subtract the difference. Draw a line horizontally at the apex on piece 4. The the difference out at this point.
Make the same shortening adjustment to pattern piece 5 as you did to pattern piece 4.
That's it! Hope it was helpful.