How to Do a Small Bust Adjustment (SBA)

HelenAshton Top, Fitting & Pattern Adjustments11 Comments

How to Do a Small Bust Adjustment (SBA)

How to Do a Small Bust Adjustment (SBA)

There are plenty of Full Bust Adjustment posts out there and different ways of doing them on all kinds of garments, but what about Small Bust Adjustments (SBAs)? If your chest or bust is smaller than a B-cup, you may want to do an SBA! Today, I will walk you through the steps of doing just that using the Ashton Top as an example. You can use this post as a reference for other patterns, too. 

First off, do you need a Small Bust Adjustment? If the difference between your high bust or chest and full bust or chest measurement is smaller than 2” (5 cm) you may benefit from a Small Bust Adjustment. The best way to assess your needs is to sew a muslin or toile. You can baste the top pieces together just to see how they fit, no need to finish seams or raw edges! 

Let’s say your full bust measurement is 34” (86.5 cm), which puts you in size 6, but your high bust falls into size 8. If you make size 6 it may be too tight in the shoulders. However, if you make a size 8 it could be too loose in the bust area and may change the look of the top or be too roomy for your liking. So let’s do a Small Bust Adjustment! 

How do to an SBA (Small Bust Adjustment)

You will need the top front and facing pieces (if you are doing the facing finish on Ashton), a pen or pencil, ruler, tape and some paper.

Start by tracing off the top front piece onto a new sheet of paper. You don’t have to do this if you want to work on the original and don’t mind printing the pattern again if needed. 

How to do a small bust adjustment (SBA) Technical Illustration

Find your bust apex by holding the bodice pattern piece up to your body and marking a dot on the nipple. It may not be perfectly in line with the dart and that is OK. Draw three lines as follows: 

  1. Starting from the bust apex to the side seam, through the middle of the existing dart (red line).
  2. Starting from the armscye to the bust apex, and then vertically down, parallel to the center front (green line).
  3. Starting at the center front and 1-2” (~2.5-5 cm) up from the bottom, draw a horizontal line perpendicular to line #2 (blue line). 

There is no hard and fast rule on where exactly these lines have to be. Just try to make your lines resemble the lines in the example below:  

How to do a small bust adjustment (SBA) Technical Illustration

Using paper scissors and starting at the bottom of the pattern, cut line #2 up to the bust apex. Pivot at the bust apex and keep cutting towards the armscye, stopping at the seam line ⅝” (1.3cm) away from the edge. Starting from the armscye, cut into the seam allowances towards your cut line, making sure to leave a small paper hinge. 

Starting at the side seam, cut line #1 almost all the way to the bust apex. Be sure to leave a paper hinge here as well! If you cut your hinge, don’t sweat it—you can just pretend it is there. 

Completely cut through line #3. 

How to do a small bust adjustment (SBA) Technical Illustration

Before you start overlapping the lines, we need to know how much room to take out. The equation is: 

(Full Bust Measurement of the size you want to make – Your Full Bust Measurement) divided by 2 

Keeping with our example from above, if your full bust measurement is 34” (86.5 cm), and the size you want to make is an 8 with a full bust measurement of 35” (89 cm), that means: 

(35” (89 cm) – 34” (86.5)) /2 = 0.5” (1.25 cm)

We will need to remove 0.5” (1.25 cm) from the pattern piece. This will give us a total of 1” (2.5 cm) removed across the whole front bodice. This is an example only and your numbers will likely be different. 

Let’s get back to the pattern. On piece A, draw a guideline (4) the required distance (number from the equation above) away from line 2 (green).  

How to do a small bust adjustment (SBA) Technical Illustration

Start carefully moving pieces B and C in towards the guideline, lining piece C to it. You will be taking room out right where you drew line 2. At the same time, start moving piece C up so that the hemline is staying straight. This will create another overlap where line 1 used to be and this will either make the dart smaller or completely remove it. Once you are happy, tape pieces B and C in place.

How to do a small bust adjustment (SBA) Technical Illustration

Move Piece D up so that the hemline and center front remain unchanged.This will create an overlap where line 3 used to be. The small bust adjustment takes out some length from the front piece since smaller chests do not need extra fabric to drape over the bust/chest. Tape piece D down. 

How to do a small bust adjustment (SBA) Technical Illustration

If your SBA did not completely eliminate the dart, you will need to redraw it. Step back from the bust apex approximately to the same spot where the original dart began and draw in the new dart legs by connecting the original dart opening at the side seams to the dart point. Redraw the dart hat. 

How to do a small bust adjustment (SBA) Technical Illustration

If your bust adjustment completely closed the dart, that is OK too! You no longer need to adjust or sew the dart, but you will need to redraw the side seam.

How to do a small bust adjustment (SBA) Technical Illustration

The next step is to make adjustments to the front facing piece. Lay the front facing on top of your new front piece, lining them up along the shoulder and the neckline. You will see that the facing is a bit longer at the center front and the side seam. The armscye on the facing will also be a little lower than the armscye on the front piece.

Remove the extra width from the front. Redraw the facing side seam from the armscye to where the new side seam of the front piece is, and cut off the excess. Place a piece of scrap paper underneath the facing and trace the new armscye onto it. 

How to do a small bust adjustment (SBA) Technical Illustration

Congrats! You just did a Small Bust Adjustment (SBA)! 

About the author

Helen

Helen Wilkinson is the designer and founder of Helen's Closet Patterns. She also co-hosts the Love to Sew Podcast! Helen is obsessed with all things sewing and strives to share her passion and knowledge with the sewing community.

11 Comments on “How to Do a Small Bust Adjustment (SBA)”

  1. Hey Helen, thank you so much for your lovely post. One thing that would really help me would be some input on how to assess if I need to do a SBA or not (besides tight shoulders). Any lines or issues I have to look out for in specific? As I am a beginner it is sometimes still difficult for me to find the source of a problem

    1. Hi Lydia,

      Thanks for checking out this post! I think the most common thing you can look out for is a baggy-ness across the chest where the bust darts are. If this area seems loose and the darts are drooping, you have too much room in the chest and would benefit from this SBA adjustment!

  2. Thank you so much for this tutorial. Doing a SBA will really improve the fit of my me made clothes. I want to try this on my next gilbert shirt.

  3. This is BRILLIANT….thank you! I have always said that are a couple million FBA and maybe TWO SBA! I totally reworked a princess seam car-coat into a double-breasted/overlapping jacket for my DIL. Like me, she needs a SBA. The only thing I had trouble with was getting the front to look smooth and not caving in… I ended up taking out different amounts on the center-front and side-front in the bust area and got it pretty good. But I’ll bet after this post I could do better because I’m understanding better what all happens to the flat pattern. I’ve been sewing over 50 years and love your podcast and patterns (long live the York Pinafore and a billion hacks!)

  4. Oh thanks for this post !! That’s exactly what I think : many FBA and when you have a cup A , your shirt/dress looks so stupid with its empty pointy spaces for bust !!!

  5. Hi Helen! I just finished my first Ashton – Woohoo! It’s my first garment in decades. (Sewing all those masks this past year got me interested again and I chose the Ashton as my first make!!).
    I was excited to see this post about the small bust adjustment, but I’m not sure that’s what I need. Do you have a moment to point me in the direction of resources about diagnosing fit problems?
    As I am a beginner, I don’t know what to call the things I see as being problematic. I have a little bit much fabric at the front of the arm and top of breast. My dart is also a bit too high.
    Looking at your diagram and assessing my pinching and tucking, I’d say that a second dart where you have drawn line 2 indicates a possible “fix” for my next version — but I would like to figure out how to adjust the pattern properly. (I graded from a 12 at shoulders and high bust to a 14 at full bust and dart. I added 6 inches for a tunic length at your ‘add length here’ line and drew a straight line to grade from bottom of dart on to a 20 at the hips).
    I’m super excited to make about 5 of these for a summer wardrobe, but I want to get the fit right. I’d be grateful for any direction or resources.

  6. Hi Helen! These SBA instructions will transform my sewing – thank you so much. I’ve just used it to alter my Ashton pattern and the result is wonderful! My previous Ashtons were nice but now I can make garments that fit perfectly. I’m going to try your method in future on all my patterns that feature bust darts.

    Additional thanks for helping me on my sewing journey. I began in the first UK Covid-lockdown ordering a sewing machine online and your York Pinafore was the first pattern I came across that was both desirable and doable for a beginner. Many months and many garments later my love affair with sewing continues to grow… Thanks again and best wishes!

    1. Hi Lisa,

      Thanks so much! I’m so glad to hear the SBA post was helpful for you and that you got into sewing with York! That makes me so happy 😀

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