We recommend making two pattern adjustments before constructing your first muslin. The first is the vertical length from your shoulder seam to the apex of your bust. This article walks through the adjustments needed to shorten the pattern in this area.
Let’s take some measurements
In the photo of pattern piece A-Front Top, notice that the seam lines are marked with dashed lines on the pattern. I have placed a tape to measure straight up from the bust apex mark to the shoulder seam. Be sure to stop measuring at the seam line, as you’re looking for the length of the finished shirt from shoulder to bust point. The length here is 10-1/2 inches.
This is my dressform, standing in for you in this example. Measuring the same location on the model, I get a length of 10- inches from the bust point straight up to where I want the shoulder seam to fall. Since the difference between these two measurements is greater than 1/4 inch, I want to shorten the pattern so the bust apex mark falls at the same level as the bust point on the model’s body.
The measurements we have for the example are:
1/2″ difference, with the body being shorter than the pattern
Remember, if the difference between the measurements is 1/4 inch or less, you don’t really need to make this adjustment.
With our measurements in hand, we’re ready to adjust the pattern
Squaring up to the center front, draw a horizontal line through the bust apex mark. Then squaring from the line you just drew, measure up from the point of the dart the amount the length needs to be adjusted (1/2 inch in this example) and place a dot at that point. Cut along the horizontal line.
From the bottom edge of the top half of the pattern, measure up the amount the length needs to be adjusted (1/2 inch in this example). Draw a horizontal line at that point, squaring up to the center front. Tape the bottom half of the pattern along this line, making sure the center front of both halves align.
The lower half of the original bust apex mark is the new bust apex location, so highlight or circle that part for clarity.
Now we need to adjust the angle of the horizontal bust dart upward so it’s pointing to the new bust apex location. Draw new dart legs from each notch to the new, higher dart point that you marked earlier.
Close the horizontal bust dart, matching dart legs. Fold the dart down as you would with fabric, and check both sides to see whether paper needs to be added to reach the cutting line. Blend the cutting lines, and trim away any excess paper. Now your shoulder to bust apex adjustment is done, and you just need to shorten the Top Back pattern piece by the same amount you shortened the front.