How to Alter Sewing Patterns for Fit
(Mastering the FBA, Swayback, and Shoulder Adjustments)
@TheSewingWorkshopWithLindaLee
@ProfessorPincushion
@TillyandtheButtons
Step-by-Step Instructions:
Once you master basic alterations, it’s time to tackle specific body adjustments. Techniques like the Full Bust Adjustment (FBA), swayback adjustment, and shoulder width alterations ensure a truly bespoke fit without distorting the rest of the garment.
Materials Needed:
- Pattern tracing paper
- Clear acrylic ruler and French curve
- Pencils, erasers, and clear tape
- Paper scissors
- Flexible tape measure
Tips for Success:
- Diagnose fit issues using a muslin (toile) first. Don’t guess your adjustments!
- Always leave a tiny “paper hinge” when cutting slash lines to easily pivot your pattern pieces.
- Make one major adjustment at a time, tape it down, and re-assess before moving to the next.
1. The Full Bust Adjustment (FBA)
- If your sewing cup size is larger than a B/C, you need an FBA. Draw a line from the bust apex to the armhole, down to the waist, and horizontally to the side seam. Slash along these lines (leaving hinges at the armhole and side seam) and spread the pieces to add necessary width and length directly over the bust apex.
2. The Swayback Adjustment
- If fabric pools or wrinkles horizontally at your lower back, you likely have a swayback. Draw a horizontal line across the lower back pattern piece. Fold the pattern to overlap and remove the excess vertical length at the center back, tapering the fold out to nothing at the side seams.
3. Broad or Narrow Shoulder Adjustment
- If the shoulder seam falls off your arm or sits too close to your neck, draw a vertical line down from the midpoint of the shoulder seam, curving into the armhole notch. Slash and spread the pieces apart to add width (broad shoulders), or overlap them to remove width (narrow shoulders).
4. Address Darts and Seam Lengths
- Major adjustments often change dart sizes. For example, an FBA creates a larger side dart. Ensure you redraw the dart legs to meet at the new bust apex (backing off by about an inch). Also, verify that adjoining side seams (front and back) are still the same length.
5. True the Altered Seams
- After pivoting, spreading, or folding, the outer edges of your pattern will look jagged. Use a ruler or French curve to draw smooth, continuous cutting lines to “true” the pattern. Redraw any grainlines if they became misaligned.
Top FAQs for Advanced Pattern Alterations:
What is a sewing cup size vs. bra cup size? +
In sewing, cup size is determined purely by the difference between your high bust and full bust measurements (1″ difference = A cup, 2″ = B cup, 3″ = C cup, etc.). This is often different from your retail bra size. Commercial patterns are typically drafted for a sewing B or C cup.
Why shouldn’t I just cut a larger size for my full bust? +
If you choose a pattern size based on a full bust measurement, the necklines, shoulders, and armholes will be far too large and sloppy. Choosing a size based on your high bust measurement and doing an FBA ensures the garment fits your frame perfectly while accommodating your bust.
How do I know if I need a swayback adjustment? +
A swayback adjustment is needed when you notice horizontal folds or puddling of fabric in the lower back area, just above the hips or buttocks. It simply means your back curve is deeper than the pattern was drafted for, requiring you to remove excess vertical length at the center back.
