October 23, 2020

How to Do an FBA on a Dartless Knit Bodice


How do you do a full bust adjustment on a knit bodice? It’s actually easier than you’d think, and we’ll be showing you how in this tutorial!

Here at Cashmerette, we include three cup sizes (C/D, E/F, G/H) with all of our patterns so that you can get a great fit right out of the packet, and most people don’t have to do an FBA. But if you’re using a pattern that is drafted with a smaller cup size than what you need, or you are significantly bigger than Cashmerette cup sizes, you’ll likely need to do an FBA.

In this tutorial, we’re showing you how to do a full bust adjustment on a knit pattern that has no dart. If you’re using a knit bodice that does have a dart, you can follow the instructions for a darted FBA here.

Okay, let’s get started!

Prepping for an FBA

Here’s what you need on hand for doing your FBA: your front bodice pattern, some tracing paper (we like Swedish tracing paper, but anything that you can see through will do), a pen or pencil, a ruler, scissors, and some tape. It helps to be working on a cutting mat or a surface that you can tape things down onto temporarily—you’ll see why pretty soon.

We always recommend tracing your pattern piece before starting to cut into it. This is so that you can refer to the original piece later on if needed—once you cut into the real thing, it’s hard to go back.

For a knit FBA, you’ll want to start by sewing up a muslin. This is the best way to determine how much length you’ll want to add, because—as you’ll see with your muslin—the hem rides up in the front due to your bust. It’s hard to know how much that adjustment should be without a muslin.

When making your muslin, be sure to use fabric that is similar in weight, drape, and stretch to your final fabric. If you’re working on a knit bodice, you should be using a knit fabric for your muslin—not actual muslin fabric. Many knit garments are designed with negative ease so that they stretch around your body, and if you make your muslin out of a woven fabric, it’ll appear as though the garment isn’t big enough, although it should be if you made it out of a knit.

How to do a knit FBA

1. Start by trying on your muslin. Stand in front of the mirror, facing to the side, and measure how much the hem rides up in the front.

2. Now take your bodice front piece, and draw a horizontal line across the pattern piece at the height of the bust apex—this is where your bust notch is, if your pattern piece has a bust notch.

3. Next we’re going to cut the pattern piece into two pieces at that line, and then we’ll side the bottom piece down by the amount of height we determined we needed in step 1. Make sure the two pieces are parallel to each other, and lined up at the center edge. (It might help to tape the pieces down to your work surface to keep them aligned.)

4. Now we’re going to trace the new pattern piece. At the side seam where there is now a gap, we’re going to add a slight curve—essentially, a boob bubble. This helps create additional width for the bust. This bit is more of an estimate, but we usually recommend adding about 1/2″ to 3/4″. Add two notches at the top and bottom of what used to be the gap.

And there is it! Our new front bodice piece with our knit FBA included.

Sewing your garment

You may have noticed that now our front and back side seams aren’t the same length. Since we’re working with a stretchy knit, we can ease in the extra length of the front piece, which creates a slight gathering effect that isn’t visible when you wear your garment. Here’s how to do that:

1. Start pinning your front piece to your back piece at the hem, going up to and stopping at the bottom notch.

2. Pin from the other side as well, going from the armscye and stopping at the top notch.

3. When you go to sew the two sides together, start at the hem and sew regularly until you get to the bottom notch. At that point, you should gently stretch the back piece until it lines up with the front piece, and continue to sew. When you get to the second notch, stop stretching and sew the rest of the seam as you would normally.

And that’s all there is to it! A knit FBA is surprisingly simple, but very effective if you need more bust room in your garment.

Want to learn more about fitting clothes to your body?

Check out our Fitting for Curves: Pattern Adjustments for the Upper Body online workshop.

One thought on “How to Do an FBA on a Dartless Knit Bodice

  1. Su says:

    Thanks for such comprehensive support! I’m making my peitite, but busty, best friend a Concord tee for Christmas (awesome meerkat cotton/spandex fabric) and want an awesome outcome and i feel confident i will achieve that outcome thanks to such great spport.

Let me know what you think!