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.
11 thoughts on “How to Do an FBA on a Dartless Knit Bodice”
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.
This was so helpful! I’ve been trying to alter a pattern for a basic tank top, something I thought would be easy. Half a dozen versions in, this was the final piece of information I needed to make it perfect! Thank you!
I wish there were illustrations of the pinning and easing steps. I cannot wrap my brain around how to ease 1/2-3/4” on the front into 0” on the back. Wouldn’t the notches that mark the vertical gap on the front be a single point on the back? If the pinning stopped an inch before each notch, I understand how to ease in the extra, but I don’t get it as written (here or in the book).
You are stretching the back while sewing, so that the front and back are the same length on the sewing machine.
I understand that the back must be stretched to match the front length. I’m trying to determine where the stretching happens. As I read the instructions, it seems that I am pinning without stretching from hem to bottom notch on front piece, which will line up with notch on back piece, and pinning without stretching from armscye to top notch on front piece, which will also line up with the notch on the back. This leaves no material on the back piece to stretch. Is the stretching of the back piece actually happening in the inches before and after the back notch or between the back notch & armscye or somewhere else?
If you measure down from the armscye to where the first notch is where you did the FBA, the stretching starts there.
Thank you for trying to help me sort this out. If the back piece is not stretched above the back notch, that means the stretching occurs below it. Now I need to understand how much of the back edge is stretched to match the length of the front edge. Am I easing that extra front length into the entire length between the back notch and hem? Or am I pinning up from the hem without stretching to a few inches below the back notch & lower front notch, then easing the extra front length into the remaining inches below the back notch?
Your second explanation is the correct one
I’m so pleased to see this on your blog now too. I learned this method from you in your Craftsy class some years back, and use it constantly. It’s so simple, yet so effective. Thank you so much for sharing it with us.
Hi, I need some help, I tried to make the full bust adjustment for the saybrook tank but it’s not a success so far
I made the size 20, and I had a lot of excess fabric at the armscye, like a dart should be here, and the hem was riding up in the front. I followed the method and added the 6,5 cm at the front pattern.
The problem is I can’t stretch the back to line up with the front when I’m sewing the pieces together (or else I have to make pleats?) there is too much fabric now at the front, and on the numerous muslins I made, the few time I did manage to sew the back and the front together (by distributing the extra from the top notch till the waist notch) I had a lot of wrinkles and “loose” fabric under my arm at the top of the side seam, like I shouldn’t have add the 6,5 cm?
Am I doing something wrong? I would gladly have some help on this issue I’m out of ideas! Thank you!
Hi Vav, I replied to your email about this a few days ago with some follow up questions. I’m happy to help you sort this out over email!
-Ayelet at Cashmerette