How to do an FBA on Princess Seams

Can I get a show of hands for those that dread doing FBAs? Let’s be honest though… it’s not the FBA that’s the challenge. It’s finding the way to do FBAs on things other than a standard T-Shirt (ahem Princess Seams)! I’m here to help! **puts on superhero cape**

Let’s walk through this. Just imagine me holding your virtual hand through each step of this process!


First things first. How much fullness do you need to add to the pattern to accommodate for your Full Bust? Take your Actual Chest/Bust (Full Bust) Measurement and subtract the Chest/Bust measurement listed on the Size Chart for the size you’ve chosen (based on Upper Chest Girth, remember?). So….

Since you have two sides (because of your two breasts of course), you will divide the Total Fullness Needed in half and that is what you will add to your pattern piece. For the purpose of this example, we will be adding 2” to our pattern piece for a total Full Bust Adjustment of 4”.

We are going to start with the Side Front Pattern Piece. To make our dress more manageable, we are first going to chop it off at the waist. Those notches are shown below as 1 .

Okay, now we’re ready to begin! Let’s dive in, shall we?

Step 1:

Draw in a 1/4” seam allowance along both the Side Seam and the Princess Seam of the Front Side Panel.

Step 2:

Connect the Waist Notches on either side of the pattern piece with a straight line and cut it along that line. Set the bottom part of the pattern piece aside for use in a future step.

Place a dot on where you believe the fullest part of the bust line is. This will be approximate. The dot will go on the seam allowance line.

Step 3:

#2 – Starting approximately 1/4 of the way down the armscye, draw a straight line to the Bust Dot.

#3 – Starting approximately 1/3 of the way down from the edge of the armscye to the waist notch, draw a straight line to the Bust Dot.

#4 – Starting from the waist notch at the seam allowance, draw a straight line to the Bust Dot.

Step 4:

Draw a horizontal line 1” above the Waist on the Princess Seam.

Step 5:

Now it’s time to make the first cut! Cut along the GREEN line starting at point “A”, through the Bust Point, and ending just before Point “B”.

Don’t cut through the armscye. You want a little bit of the paper left to “hinge”.

Step 6:

Next, cut the line that goes from the side seam to the Bust Point making sure to not actually cut through the Bust Point so you have a remaining “hinge”.

Step 7:

Place paper underneath your pattern piece to begin.

Using your hinge points, position your sliced up pattern piece so that you achieve the desired fullness adjustment. In this example, it is 2” for a finished 4” adjustment.

Step 8:

Cut off the 1” long piece along the princess seam (from your previous guide mark) and line it up so that the guide marks are once again in line as shown in red.

Now, tape your sliced up pattern in place.

Step 9:

Cut the excess extra paper off to reveal your incredibly strange looking new pattern piece! Don’t fear, we’re not done yet…

Step 10:

Now it’s time to close your bust dart. Draw a straight line from the bottom corner of your bust dart, through your Bust Point, and end at the Princess Seam.

Step 11:

Cut your pattern piece along the line you created in the previous step. You will now have 2 separate pieces. Rotate the top piece counter clockwise so that points “C” and “D” are together and the 2 green lines are on top of one another.

Step 12:

Draw a curve (shown in red), to reconnect your Princess Seam together. Tape additional paper underneath the pattern to close the empty space.

Last, even out the armscye to remove that funny little point on top.

Step 13:

Remember that now although we have added fullness to the Full Bust, we’ve also added it to the waist. Let’s remove that now. Because your piece may be at a tilt like mine, let’s make this an accurate adjustment, shall we?

Measure the distance of “E”. Take that number and measure the same distance in from the bottom side seam, “F”. Draw a line from the bottom of the Bust Dart to the inner end of “F”. Trim off the excess triangle.

Step 14:

We’re almost done, I promise! Let’s connect the modified side front top of our dress to the side front bottom we cut off before we began.

Tilt the waist seam of the dress bottom until it fits nicely with the side front top. Ahhhhh…. she is a beauty!

Step 15:

Hold on a second, What about the Front Center of our Dress? Yep, one LAST step.

As you can see, the Princess Seam of our FBA is much longer than it was originally. In order for our Side Front Piece to Fit our Front Center Piece we have to add some length to it. Measure each Princess Seam by walking your measuring tape around each seam. As you can see, we need to add 4” of height to our Front Center Piece and we will do that directly at the waist. Remember, that’s the first notch.

Step 16:

Split your pattern piece and add the 4” of length.

Step 17:

Now take a deep breath, stand back and admire your work. You deserve a glass of wine… Cheers!


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