Sewing a Small Bust Adjustment (SBA)
Let’s continue with our Bust Adjustment series! Today we will walk through every step of doing a small bust adjustment (SBA) on a pattern piece with no dart. This is often on knit fabric but could be a woven pattern without darts as well.
If you have not already, take a look at the Bust Adjustment 101 post, for all the details on when to do the bust adjustment, and how to know what adjustment needs to be made. This will help you calculate exactly how much you need to remove from the pattern piece in your SBA.
A small bust adjustment is done when the full bust to upper bust difference is SMALLER than the pattern is drafted for. By doing the SBA, you are removing excess fabric from the bust area, without making the rest of the bodice smaller. This gives a perfect custom fit for your individual shape!
Let’s Get Started!
Preparing the Pattern piece
You will need to start with TWO of your pattern pieces. The original for you to refer back to later in the process, and a tracing that you can cut up.
Begin by marking the apex point on the pattern piece. Some patterns will include this marking. If yours doesn’t, or for a custom fit, hold the pattern piece to your body and mark the point of your apex of the fullest part of the bust. Do this while wearing the undergarments you plan to wear under the finished garment.
Next, draw the lines that will be used for cutting the pattern. The first line runs from the apex point straight down to the hem. The second runs from the apex point horizontally across to the side seam. The third goes from the apex point to about 1/3 of the way up the armscye from the armpit point.
Begin cutting the pattern piece starting at the hem, cutting up the first line, through the apex point, and continuing through the line that runs to the armscye. STOP at the armscye edge, do not cut through this point (shown in red in the second drawing). This will be a hinge.
Then, cut from the side seam on the line that runs horizontally to the apex. STOP when you get to the red point at the apex. This will be the second hinge.
The following drawing shows what it should look like when you have finished cutting.
You should now be able to gently rotate the hinged pieces as shown above.
Starting the SBA
If it is helpful, label the three pieces of the bodice as A, B, and C as shown above.
Draw a vertical line on piece A, parallel to the cut between A and C, the distance away from the line of C that you need to adjust. In this example, I am adjusting the pattern piece by 1/2″. (Unsure how much to adjust? Refer back to Bust Adjustments 101.) The vertical line I drew is 1/2″ away from the A/C cut line, as that is the amount I need to reduce from the pattern piece.
Keeping B and C together, rotate towards A on the armscye hinge. Rotate until the apex point of B/C touches the line you drew.
Tape piece B to piece A, leaving C free to move.
Rotate C on the apex hinge, until the vertical line of C is exactly lined up with the vertical line you drew on A. C now overlaps both A and B. Piece C should overlap piece A the 1/2″ you needed to reduce. Tape C in place.
Next, you need to adjust the hem line. Because A and C were lifted up and in, A is now too long. Draw a line across A, either on the lengthen/shorten line of the pattern piece, or a couple inches above the hem line. Cut across this line. Shift the cut piece up until the hem line of A matches the hemline of C. Tape in place.
Draw a line around your new pattern piece, smoothing out the edges. Cut out. You are almost done, but not yet!
Finishing the SBA
Lay your new pattern piece on top of the original pattern piece. (Remember how you had two copies of the original?) The new one will match the original on the fold line, the neckline, the shoulder, and the top of the armscye. Then you will notice the new pattern piece is smaller through the bottom of the armscye, the side seam, and the hem.
You need to bring the waist line back out to the original line now, or it will be too small in the waist!
Starting at the bottom of the ORIGINAL side seam, blend out to the NEW front center hem. This creates your new hem line. It will be the same as the original where it meets the side seam, but will be shorter than the original at the center line. This is because a small bust adjustment takes up some of the center fabric that was drafted to go over a fuller bust vertically.
Then, starting at the bottom of the side seam, blend up to meet the new armpit point. Stay on the original pattern line through the waist, blending into the new line in the bust. From the armpit, stay on only the NEW line of the armscye.
The red line above shows how to do this. Cut the pattern piece out on the new (red) line.
That’s it! This is the final pattern piece with completed small bust adjustment.
At this point it is a good idea to measure the side seam and compare it to the side seam of the back bodice piece of the pattern. Especially for a knit pattern, the difference might be negligible enough to leave, but you may need to shorten the back bodice side seam to match. Do this on the pattern’s lengthen/shorten line.
You are done!
It may seem overwhelming when it is new, but practice makes perfect! Once you have done an SBA a couple times, it will feel so much less intimidating. You may want to trace off a couple copies of a bodice pattern and just practice a few times! That way you won’t worry about doing it perfectly the first time. Before you know it, you’ll be doing every SBA with ease.
In the rest of this series, we will cover doing an SBA on a pattern piece with darts, and also a full bust adjustment on patterns with and without darts.
Remember, you’ve got this! And we are here to help. Join our Facebook group for support and encouragement in all of your sewing endeavors!
