How to Make a FBA (Full Bust Adjustment) on Princess Seams

In order to get the best possible fit on your handmade garment, you often have to make some adjustments to the pattern: lengthen or shorten some seams, add a little width to the hips, take the waist seam in 1/2″…

One of the most feared, but most efficient, adjustments is the full bust adjustment, “FBA,” along with its twin, the small bust adjustment. Just looking at the diagrams for these fixes might give you a headache. Truth be told, that’s what I thought too before looking at it for real. That’s when I realized that these charts could make sense and weren’t so terrifying after all!

Follow along with this a step-by-step photo tutorial to learn how to make a full bust adjustment on a princess seam, so you too can conquer the adjustment beast!

Full Bust Adjustment on Princess Seams

Before you begin…

First of all, you want to make a muslin of the bodice for your pattern to know how much you need to increase the bust area. If your bust size is 1 or 2 sizes higher than your waist size, you might need a FBA. Another good indication is to look for the cup size on the pattern, as most patterns are designed for a B or C cup.

For a pattern similar to one in the picture above, you would choose your size according to your waist measurements. Let’s say that, for example, your waist is 29″ (size 40) and your bust is 38″ (size 42). The bust measurement for size 40 is 36,” so there is a 2″ difference. We’ll cut the pattern in size 40 and add 1″ (at each bust seam) to make the full bust adjustment — without ever increasing the waistline or the neckline.

Marking your pattern piece

Step 1:

Take you pattern bodice front and side-front pieces. Draw the seam allowances and all the marks (notches, grainline…).

On the bodice side-front piece, we’re going to draw 3 lines:

  1. From the waistline to the fullest part of the bust.
  2. From 1/3 of the armhole (remember that the armhole is made of the the front and side-front bodice pieces) to the fullest part of the bust.
  3. From the fullest part of the bust, draw a diagonal line toward the side seam allowance, like a dart.


Cut lines 1 & 2

Step 2:

Cut lines 1 and 2 and stop when you reach the seam allowance.

Cut the seam allowance

Step 3:

Cut the seam allowance, but make sure it’s still attached (see above).

Cut line 3

Step 4:

Cut line 3 and stop just before you reach the fullest part of the bust.

Matching seam allowances

Step 5:

Tape the princess seam to a piece of paper and pivot the pattern along lines 1, 2 and 3, so that the opening at line 1 measures the 1″ increase we need. Make sure the 1″ increase is even all the way down line 1. Tape the pattern in place on the paper.

Draw parallel waistline

Step 6:

As you can see, the waistline is not even. Draw a line parallel to the waistline on the princess seam part.

Cutting and piecing custom pattern piece

Step 7:

Cut along the line and place the small piece on the continuity of the waistline, 1″ from line 1. Tape.

Rough cut of new pattern piece

Step 8:

Cut roughly around the new pattern piece.

Draw line extending from the princess seam

Step 9:

Draw a line extending to line 3 of the princess seam.

Cut line 3 again

Step 10:

Cut along line 3 until you reach the fullest part of the bust.

Close and tape the dart

Step 11:

Close the “dart” and tape.

Making a FBA pattern piece

Step 12:

Cut the line 3 from the princess seam to the fullest part of the bust, leaving a pivot. Place a piece of paper under the spread “dart” and tape.

Finishing your FBA pattern piece

Step 14:

We need to take 1″ in at the side seam to keep the waistline the original width (this is the measurement we added at the bust). Draw a new side seam starting from line 3 and ending 1″ from the waistline edge.

Taking 1" in at the side seam of FBA pattern piece

Step 15:

Now we need to add the increases we made to the side front piece to the front. Trace 2 lines at the same level you made the increases. Cut along the new side seam.

Measuring side-front bodice piece

Step 16:

Measure how much you added to the side-front piece and report that on the front piece. For the bust, measure the seam allowance line, not the cutting line.

Completed FBA pattern pieces!

There you go: Your new pattern pieces are complete! We have “magically” increased the bust area without touching to the waistline, armhole or neckline.

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Want ever expert guidance and in depth lessons on how to construct the perfect fit? Check out Bluprint’s online sewing class Sew the Perfect Fit with expert sewing instructor Lynda Maynard, as she uses three real women to teach you how to adjust your pattern to your ideal measurements!


How about you? Do you often find yourself having to make a full bust adjustment? Any additional tips you’d like to share?

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