My knit patterns no longer include cup sizes. For this kind of garment, separate cup options often create more complexity than benefit. More pattern pieces, more decisions, and not always enough payoff to justify either. If you do need extra room through the bust, though, a full bust adjustment (FBA) on a knit is usually not that dramatic. It is very manageable and mildly empowering. Just try not to disappear too far down the adjustment rabbit hole. Some drag lines and folds are completely normal, and sometimes they are even part of the design. The goal is not to eliminate every ripple from a finished garment. The goal is to make something that fits well, feels good, and still brings you joy to wear.
There are many ways to do an FBA on a knit garment. This is the method I like best, based on a technique from Jennifer Lauren Vintage with a few tweaks from me to simplify it a bit. I call it efficiency, though I suspect laziness is also involved. If you would like to see the original method explained in a different way, I definitely recommend checking out her blog as well.
How do you know if you need an adjustment?
Usually, the signs are fairly straightforward: the garment feels tight across the chest, there are folds or pulling near the underarm, or the front hem is getting lifted up. None of those automatically mean disaster, but they can be a good clue that the bust area needs a bit more room.
As for how much to add, the usual woven rule of thumb is about 1" (2.5 cm) per cup size. For knits, that is often more than you need. A knit garment already has some stretch and give built in, so I usually suggest starting with about 1/2" (1.3 cm) per cup size and assessing from there.
I’ll be showing this adjustment on my free Tabitha Tank pattern, but the same general approach will work for most knit patterns.
YOU WILL NEED
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a front pattern piece
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extra paper
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Marking tool (pen, pencil, crayon…), tape and paper scissors
STEPS
1. Draw Four Lines
Find the bust apex on your pattern. How? The easiest way is to hold the pattern piece up to your body, lining up the shoulder and center front as best you can, then mark the fullest point of your bust. It does not need to be perfectly precise. We are not drafting a bra here.
Next, draw four lines from the bust apex.
- First, draw a vertical line (1) straight down to the hem, parallel to the center front.
- Then draw an angled line (2) from the bust apex to the armscye. This line does not need to hit an exact magical point on the armscye, so do not overthink it. Just aim for roughly the same area shown in the illustration.
- Draw a horizontal line (3) from the bust apex to the side seam.
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Finally, draw another horizontal line (4) somewhere in the lower part of the side section of the pattern, about 3" (7.6 cm) up from the hem. It does not need to be exact, so just make it look roughly like the illustration.
Ideally, these last two lines are perpendicular to line 1, but if they are not absolutely perfect, that is fine too. Just get them reasonably close and move on with your life.
2. Cut and Rotate Out
Starting at the hem, cut up along line 1. When you reach the bust apex, pivot and cut along line 2. Do not cut all the way through to the armscye edge. Try to stop about 3/8" (1 cm) from the edge, which is roughly the seam allowance width, then make a small cut in from the armscye side to create a hinge. If you do cut all the way through, which I often do, it is fine. We will simply carry on and act like that was the plan all along.
Place a piece of paper underneath the front pattern piece and tape the center front section in place. This is the part that stays put. Rotate the side section outward to open up the pattern. Or, if you fully cut through the hinge, which I suspect some of you did, just move that section aside and line it back up as needed.
Next, draw a line parallel to line 1 at your adjustment amount. As mentioned earlier, for knits, start with about 1/2" (1.3 cm) per cup size.
3. Line Up Bust Apex
Rotate, or place, the side section back into position so that the bust apex touches the line you just drew. Tape it down at the armscye and just above the bust apex.
4. Rotate the Lower Section
Starting at the side, cut along line 3, stopping just before the apex to create a hinge. If you didn’t stop, well… you already know the drill.
Using that hinge, rotate the lower side section inward until the two edges of the opening along line 1 are parallel. The lower section should now sit more in line with the upper section. Do not tape it down yet.
5. Redraw the Hem
At this point, you will see a small dart opened up at the side seam, and the center portion of the pattern will be a bit shorter than the side.
Most FBA tutorials will now tell you to draw a line through the center section, cut along it, and drop that piece down until it matches the side. That is a perfectly valid way to do it. I, however, am lazy. So instead, I simply redraw the hem from the lower point of the side section to the center front and move on with my life.
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If you have done an FBA on a woven before, this probably feels familiar. And if you have not, congratulations, you have now accidentally learned the general idea.
From this point on, you have two options. One is to call it a day and simply ease the extra front side seam length into the bust area only, not along the entire seam, when sewing the side seam. Yes, this creates a bit of gathering, but on a knit garment, it is usually very subtle and nearly invisible when worn.
The other option is to get a little fancier and make a few more adjustments. That is the route I usually take, because apparently, I do enjoy more drama after all.
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6. Close the Dart
Cut through the remaining hinge at the bust on line 3, unless you already took care of that by accident earlier.
Slide the entire lower side section of the front upward, keeping it on the adjustment line, until the dart closes completely. For now, tape down only the section above line 4.
7. Cut, Slide Down and Ta Da!
Cut through line 4 completely. Yes, all the way through. Slide the lower section down, keeping it aligned with the adjustment line, until it sits level with the front section. Then true up the hem and side seam, and cut out your new front piece.
You’re done. As always, I recommend testing the adjusted pattern in a muslin first. But if you are feeling confident, by all means, skip straight to the real version. If that goes sideways, I would just like the record to show that I did suggest a muslin.