MN2102 Banksia / Pattern Alterations & Adjustments / Sewalongs / Tips & Tutorials

Banksia Sewalong: How to do full bust and small bust adjustment

I’ve had a lot of requests for tutorials for doing a full bust adjustment (FBA) and small bust adjustment (SBA) for the Banksia pattern, so I wanted to make sure we had a tutorial on how to do them on this pattern, specifically.

We’re going to run through what exactly a bust adjustment is, how to know if you need one, how to calculate the amount of one and then how to actually do one! That’s a lot to cover, but don’t worry, it’s way less scary than you might think! Shall we get started?

What is a bust adjustment?

Most sewing patterns, including our 0-20 (or in Banksia’s case, the XS-XL range) are drafted on a B cup block and most Curve patterns like our Curve 14-30 range are drafted for a D cup. If your bust is significantly larger or smaller than the cup size a pattern is drafted for you may notice some fit issues when wearing and as a result, need to adjust your pattern to better fit your bust.

When you need to add room to the bust of a pattern, that’s called a Full Bust Adjustment or FBA.

When we’re talking about reducing the bust of a pattern that’s called a Small Bust Adjustment.

I’ll first show you how to measure and prepare for both types of adjustments, because those first few steps are the same. And then we’ll delve into how to do an FBA and then SBA on a side bust dart like the one in the Banksia Blouse.

Determining if you need a bust adjustment

So how do you figure out if you need a bust adjustment? There are a couple of ways to find out!

Making a muslin

If you’ve already made a muslin using your full bust measurement to choose your size, but you notice fit issues like strange draglines or gaping around the armscye, the dart point hitting you too high, the waistline being much too high at the front compared to the back etc. then you may need a bust adjustment.

Checking the size chart

If looking at the size chart you notice that your full bust measurement is in a significantly different size bracket than your waist measurement. For example, if your Bust measurements puts you at a 20 but your waist puts you at a 16 you might need an adjustment.

Comparing high bust to Full bust

Sewing cup size is determined by comparing the full bust measurement to the high bust measurement in inches. This may or may not correlate with your bra cup size which is calculated using your underbust measurement, so it’s worth measuring yourself rather than working off the expectations of your cup size.

Full bust – High bust = cup size

The number of inches between your full bust and high bust measurement will determine your cup size.

A cup = 1” difference
B cup = 2” difference
C cup = 3” difference

So in order to determine if you need an adjustment, you can measure your high bust and compare it to your full bust. If the difference is significantly larger or smaller than the pattern is drafted for you’ll likely need to do an adjustment

Calculating the FBA and SBA amount

So now that you know whether you need to do a bust adjustment, we need to figure out how much of an adjustment to make and what size to cut out of the pattern!

There are two easy ways to calculate the size of your bust adjustment.

The first is using the high bust measurement. After measuring your high bust add on 2” (if using a pattern drafted for a B cup like Banksia). We’ll call this your equivalent bust for purpose of explanation. Choose your pattern size based on this “equivalent bust” measurement. Your full bust adjustment less the calculated equivalent bust measurement is the amount of your FBA or SBA.

For example, if your full bust measurement is 42” and your high bust measurement is 38”. Then your equivalent bust measurement would be 38” + 2” = 40”. This means for the Banksia pattern, you would cut out a size L (or a size 14 in our 0-20 size range patterns). The difference between your full bust and the equivalent bust is 2” so the amount of your bust adjustment is 2” total. We would then halve this number to determine the adjustment to the half pattern, and would adjust the front pattern piece by 1” (2.5cm).

The second method means comparing the different size bands of your body to the sizing chart. If your waist measures as a size L but your full bust measures at a size XL then you would cut a size L and make your adjustments on that. The size of the adjustment would be the difference between the bust measurements of these two sizes. So in the example we have been using the difference between a size L and size M bust is 2”, so your total full bust adjustment would be 2”. We would then halve this number to determine the adjustment to the half pattern and would adjust the front pattern piece by 1” (2.5cm).

Worth noting

You won’t necessarily get a bad fit choosing your pattern size on your full bust if you aren’t too far from the cup size drafted. For example, I measure as an A cup, with a 1” difference between my high bust and full bust. However, I never bother with an SBA as experience has taught me I can get away with choosing my size based on my full bust without noticeable fit issues.
Keep in mind that just because your measurements aren’t exactly the same as the pattern doesn’t mean you necessarily need an adjustment unless you see fit issues. I would recommend making adjustments from the start if you have a significantly different cup size than the pattern is drafted for.

So, now we know if you need a bust adjustment as well as how much you need to adjust by, so let’s get started on what we need to do to make that happen!

To prepare your pattern piece for either adjustment, start off by marking your armscye seam allowances, 5/8″ (1.5cm) from the edge of the pattern. Then the fun part – let’s draw some crazy lines all over our patterns! Kidding. They’re not crazy, they have very specific purposes, so let’s run through them now.

  1. First, draw a line through the centre of your dart and beyond the dart point by 1″ (we’ll call this line 1). At the end of this line, 1″ (2.5cm) past the tip of your dart, is the pattern’s bust apex (the point which should align with the most prominent part of your bust). Mark that point.
  2. Next draw a line from this point, the bust apex, to your armscye, about 1/3 of the way in (this is line 2). Conveniently, the lower notch on the armscye of this pattern is about 1/3 of the way in.
  3. Draw a line downwards from your bust apex straight down to the bottom of the pattern. This line should be parallel to the grainline & centre front fold line (line 3).
  4. Lastly, draw a line perpendicular to the grainline about 1/2 way down between the bust apex and the hem (it doesn’t matter too much where you draw this line, just don’t go too high and interfere with your dart). This line (line 4) should hit line 3 and the edge of the pattern.

Now we are going to slash along these lines. Take a deep breath, and make a cup of tea if you need it – you can do this!

Cut line 3 from the bottom of the pattern to the bust apex, then along line 2 up to the armscye, but stop just before the stitch line we drew earlier! (5/8” or 1.5cm from the edge of the armscye).

We are going to cut the rest of line 2 from the other side. Make the small snip from the pattern edge to the stitch line, but again stop just before the line. This little bit that we have left is going to act as a hinge, so don’t cut all the way through. The reason we are using the stitch line as our pivot point (instead of the pattern edge) is so the armscye will stay the same size, and our sleeve will still fit perfectly and won’t require adjustments.

Next cut line 1 from the side seam towards the bust apex. Do not cut completely through the pattern paper at the bust apex though. Once again, we want to leave a bit of paper to use as a hinge.

From here we can now add room for an FBA or remove bulk for an SBA. Let’s start with the FBA!

For an FBA, you will spread the centre slash line (line 3) by the size of your bust adjustment. Make sure you keep the slash lines parallel (i.e. keep the distance the same all the way down). For this example, I’m going to use an adjustment of 1″. This will also open up your dart wider because it is on that hinge you left. Place paper underneath and tape everything in place except for the section below line 4.

We’re now going to redraw the dart legs, which will still start in their original positions on the side seam at the dart opening, but now end at the end of line 1 (our old bust apex).

Now you need to fix the hemline as the centre front will now be slightly shorter. Cut along line 4, cutting completely through – then move it down till it is in line with the new hemline. I like to use my ruler to keep it straight. Tape everything in place and draw in the new pattern edges in the gaps we’ve made. You can also smooth out the curve of the armscye if it has been disturbed.

Lastly, to true the dart extension so it will sit flush with the rest of the seam, fold up your dart as if it were being sewn and cut along the pattern edge. The dart intake will be trimmed underneath to form the dart extension that will now be the perfect shape to align with the pattern edge.

And voila! You can now open everything back up and admire your new fuller bust dart!

Note: using this method will also increase the waistline width of your blouse, see below for our discussion on amending this.

So for an SBA, you’ll be using the same slash lines, but you will be overlapping instead of spreading.

Overlap the pieces of slash line 3 by the amount of our SBA – for this example I used 1/2”. Keep them parallel along the grainline. As you can see, this will also cause your dart to overlap and therefore become smaller.

With your overlap taped & secured, it’s time to redraw your dart. Draw a line from the bust apex to the side seam, ending at the point where the overlapping dart sections intersect – this is the centre line of your dart. Measure 1″ (2.5cm) along the centre line, in from the bust apex, to mark your new dart point.

You can then draw your new dart legs, starting at the original dart openings on the side seams (one of which may be hidden under the overlap), to the new dart point. Trim the excess paper along the pattern’s edge.

Now you need to fix the hemline as the centre front will now be slightly longer. Cut along line 4, cutting completely through – then move it up, overlapping till it is in line with the new hemline. I like to use my ruler to keep it straight. Tape everything in place. You can also tape a small piece of paper under the gap that has opened up at the armscye, redrawing its curve and trimming away any excess.

And that’s your SBA done! How easy was that?

Note: using this method will also decrease the waistline width of your blouse, see below for our discussion on amending this.

So, as I mentioned at the end of both adjustments, using these methods will also increase or decrease the width of the waistline by the same amount as your bust adjustment. Since Banksia is already a loose-fitting blouse, in most cases this won’t matter too much, but if you would like to correct the incidental adjustment, you can!

To do this, simply add the missing amount or remove the added amount to the bottom edge and draw a new side seam line up to the bottom of the dart leg. It’s as simple as that!

One final note though – if you are making your adjustments on a different pattern, like Dove for example, which has specific hem details that the above trimming or adding correction may disturb, there is an alternative method you may prefer.

Instead of maintaining the entire bust adjustment for the full length of the bodice, this method involves keeping the bottom edge of line 3 hinged, to maintain the hemline, and only spreading or overlapping the full amount of the adjustment amount at the bust apex. This method does affect how the dart shape changes slightly – making the FBA dart wider and the SBA dart narrower – but will otherwise keep the hem mostly undisturbed.

So that’s it! I hope you found today’s tutorial helpful and that you’re feeling ready & confident to go tackle those bust adjustments! If you have any questions, or would like to share your bust adjustment experiences – don’t forget to post in the comment section below.

Happy sewing xx


Some other tutorials you might like to check out:


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About Author

Holly writes part time for the Megan Nielsen blog– sewing like crazy, creating tutorials and sewalongs. She has been sewing since she was a little girl, and has her degree in apparel design. Now she’s a stay at home mama, and spends all her free nap times at her sewing machine.

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11 years ago

I just received my pattern and I’m excited to start sewing! However, I just realized that an XS is one size too large for me. My measurements are the next size down: 32/24/32. Would it be possible to do a tutorial on how to make this pattern overall one size smaller?


Marina Dias
Marina Dias
11 months ago

This is the best lesson I have come across on FBA and SBA. Thank you so much.