How to Do a Bust Adjustment on a Darted Bodice (FBA & SBA)
If your handmade clothes don’t quite fit right across the bust, a simple pattern tweak can make all the difference. In this tutorial, you’ll learn how to make bust adjustments on a darted bodice, including a full bust adjustment (FBA) and a small bust adjustment (SBA).
Whether your bodice feels tight or loose, this guide will help you get a smoother, more comfortable fit -without changing the neckline or shoulders.
What is a bust adjustment?
A bust adjustment is a pattern alteration that changes the fit at the fullest part of the bust while keeping the rest of the garment the same size.
It can help you get a better fit if your bust is particularly larger or smaller than the cup size the pattern has been designed for.
- Full bust adjustment (FBA): adds room at the bust
- Small bust adjustment (SBA): removes excess room
Can I use this on any pattern?
This method can be used for bodices with bust darts, such as the Lyra shirt dress or Nell blouse and dress. There are different methods for bust adjustments on dartless bodices and princess seam bust adjustments.
Do you need a bust adjustment?
You might need an FBA if:
- The fabric feels tight across your bust
- There are strain lines across the full pust or pointing towards it
- The bodice rides up at the front
- Your bust is larger than the pattern's dressmaker's cup size
- You made a garment based on your full bust measurement and it's too loose around the shoulders and upper chest
You might need an SBA if:
- There’s excess fabric or gaping at the bust
- The bodice feels baggy at the front
- Your bust is smaller than the pattern's dressmaker's cup size
- You made a garment based on your full bust measurement and it's too tight around the shoulders and upper chest
If you're not sure if you need to make a full or small bust adjustment, find out the dressmaker's cup size of the pattern, or make a quick toile of the bodice and see what you think.
You may not need to adjust the bust on looser-fitting garments that include a lot of ease. Check how much ease has been added to a pattern by subtracting the body measurements from the finished garment measurements.
Understanding dressmaker's cup size:
Dressmaker's cup sizes are based on the difference between high bust (upper chest, under your arms) and full bust measurements.
- A cup = 2.5cm (1in) difference between high bust and full bust
- B cup = 5cm (2in) difference
- C cup = 7.5cm (3in) difference
- D cup = 10cm (4in) difference
- E cup = 12.5cm (5in) difference
...and so on.
On most Tilly and the Buttons sewing patterns, sizes UK 6-16 (US 2-12) have been drafted for a dressmaker's B cup, while sizes UK 18-34 (US 14-30) have been drafted for a dressmaker's D cup. On our older patterns that come in sizes UK 6-20 or 6-24 only, all sizes are for a dressmaker's B cup.
If the Body Measurements chart in the pattern includes the high bust as well as the full bust, you can work out what dressmaker's cup size the pattern has been drafted for by subtracting the former from the latter.
Mistake to avoid: Don't confuse dressmaker's cup sizes with bra cup sizes, which are based on the difference between the full bust and under bust.
How much should you adjust?
Measure your high bust (upper chest, under your arms) and full bust (around the fullest part). Calculate the difference between these two measurements, and what dressmaker's cup size that makes you.
Compare this to the dressmaker's cup of the pattern you're making, in the size you're making - or the difference between the high bust and full bust if they're included on the body measurements chart.
If the pattern is designed for a B cup (5cm [2in] difference between high bust and full bust), but you are a D cup (10cm [4in] difference), you should make an FBA and add 5cm (2in) to the bust. If you are an E cup, you'll add 7.5cm (3in), and so on.
If the pattern is designed for a D cup, but you are a B cup, you would make an SBA and subtract 5cm (2in) from the bust.
It's best to make a bust adjustment to a pattern that suits your high bust measurement, so the upper chest and shoulders don't end up the wrong size.
What you’ll need:
- Darted bodice pattern piece
- Paper scissors
- Tape or glue
- Extra paper
- Ruler (or pattern master if you have one)
- Pencil
I’d suggest tracing your pattern first so you can go back to the original if you need it.
How to do a full bust adjustment (FBA)
Step 1: Mark the bust point
Hold the front bodice pattern piece against your body, the shoulder line overshooting your actual shoulder line by 15mm (5/8in). Mark the fullest point of your bust - or the bust apex.
Step 2: Draw the lines
Draw lines on the front bodice pattern:
- Through dart from bust point to side seam
- Waistline to bust point (parallel to grainline), then bust point to armhole (about 1/3 of the way up)
- Horizontal line near the bottom of the pattern, between vertical line and centre front
Step 3: Cut and hinge
Cut along the lines. When cutting the bust dart line, stop just before the apex. When cutting the armhole, cut from the armhole to the stitch line, then up the other way. Leaving little hinges will allow us to keep these positions intact.
Step 4: Spread the pattern
On a new piece of paper, draw two vertical lines, the distance between them being the amount you want to add to the pattern. Remember, this is half the total width you want to add to the garment, as the pattern represents half of the front bodice.
Align the cut vertical lines on the pattern with these lines and tape or glue in place.
The dart will widen, increasing the length of the pattern. Extend the lowered bottom edge of the pattern along, and stick the remaining piece down in line with this.
Step 5: Redraw the dart and seams
Smooth out the armhole, hem or waistline, and centre front.
Redraw the dart legs, aligning the tip with the height of the bust apex.
How to do a small bust adjustment (SBA)
An SBA is essentially the reverse of an FBA - you’ll overlap the pattern pieces instead of spreading them.
Step 1: Mark the bust point
Mark your bust apex in the same way as for an FBA.
Step 2: Draw the lines
Draw the same lines on the front bodice pattern:
- Through dart from bust point to side seam
- Waistline to bust point (parallel to grainline), then bust point to armhole (about 1/3 of the way up)
- Horizontal line near the bottom of the pattern, between vertical line and centre front
Step 3: Cut and overlap
Cut along the lines. When cutting the bust dart line, stop just before the apex. When cutting the armhole, cut from the armhole to the stitch line, then up the other way.
From the bust apex away from the dart, measure the amount you want to decrease the bust by (half the total width you want to subtract from the garment), and mark this point. Draw a line parallel to the grainline from the bottom of the bodice to past this marking.
Move the bottom of the pattern under the dart until the vertical cut line aligns with the line you just drew. Tape or glue in place.
Step 4: Redraw the dart and seams
Redraw the dart legs, aligning the tip with the height of the bust apex.
Want more help with fitting?
Learn to diagnose and fix fit issues with guidance from a friendly expert in our online workshop Bodice Fitting for Home Sewing.
