A standard sewing pattern is drafted for a B-cup bust. If your bust measurement is larger than that, the front bodice will pull, gap at the armhole, or drag across the chest. The usual fix is a Full Bust Adjustment (FBA), but many people also need a Small Back Adjustment to keep the neckline and shoulders from becoming too wide. Together, these two changes produce a garment that hangs cleanly from the shoulders, skims the back, and allows proper room across the bust.
This tutorial walks through the FBA and the corresponding small back adjustment on a basic bodice block with waist darts and shoulder darts. The same method works for most woven bodice patterns, whether they have princess seams or darts.
Photo by Debby Hudson on Unsplash.
What You Will Need
- Pattern paper – tracing paper or plain paper for copying your pattern pieces.
- Ruler – a clear metric or imperial ruler, preferably 60 cm / 24 inches long.
- Pencil – a sharp HB or mechanical pencil.
- Scissors – a dedicated pair for cutting paper only.
- Tape – transparent or masking tape for piecing the altered pattern back together.
- Muslin fabric – for a test garment. Cotton muslin is inexpensive and behaves similarly to most woven apparel fabrics.
Preparation
Before you cut anything, identify the original pattern’s cup size. Many commercial patterns specify a B cup. Check the envelope or instruction sheet. If it says “B” or makes no mention, it is almost certainly a B cup. Measure your full bust and your high bust (just under the armpits, above the bust). The difference between these two measurements determines your cup size. For example, a 5 cm (2 in) difference is a B cup, 7.5 cm (3 in) is a C cup, 10 cm (4 in) is a D cup, and so on. You will be adding the difference between your cup and the pattern’s cup to the front bodice.
Trace the front and back bodice pieces onto pattern paper, including all markings: grainline, dart legs, notches, and bust point (often marked as a dot or a small cross). Do not cut the original – keep it intact for future use.
Step 1: Mark the Bust Apex and Slash Lines
On the traced front bodice, locate the bust point. If the pattern does not mark it, estimate by drawing a line from the centre of the shoulder dart straight down. The bust point is usually about 2.5 cm (1 in) below that dart’s tip, and roughly in line with the waist dart. Mark it with a clear dot.
Draw a slash line from the bust point to the bottom of the armhole, perpendicular to the grainline. This line will stop about 1.25 cm (½ in) from the armhole edge. Do not cut through to the armhole – leave a small hinge. Draw a second slash line from the bust point straight down to the hem, parallel to the centre front. Draw a third line from the bust point to the centre of the shoulder dart (not to its tip), stopping 1.25 cm (½ in) from the dart leg. Finally, draw a short horizontal line across the waist dart, about halfway between the bust point and the dart leg, perpendicular to the waist dart’s centre line.
Step 2: Cut and Spread
Cut along the first slash line from the armhole side toward the bust point, stopping at the hinge. Cut along the second slash line from the hem up to the bust point. Cut along the third slash line from the shoulder dart toward the bust point, again leaving the hinge. Now cut the waist dart horizontally along the short line you drew. This will allow the waist dart to open as you spread the pattern.
Place the cut piece on a fresh sheet of pattern paper. Tape down the shoulder side (the part above the shoulder dart) so it does not move. Now spread the bottom section downward and to the left (if you are working on a right half of the bodice) until the opening equals the amount you need to add. To calculate the spread: for each cup size above B, add 1.25 cm (½ in) for a full bust adjustment. For a D cup (two sizes above B), spread 2.5 cm (1 in). This is the total extra width needed at the bust. Tape the bottom section in place.
Step 3: Adjust the Waist Dart
The waist dart will have opened into a wider triangle. Redraw the dart legs neatly from the new dart points to the original dart tip at the bust point. The dart tip should remain at the bust point; if it shifted, move it back. The dart should taper smoothly. Trim any excess paper.
Step 4: True the Armhole and Side Seam
The armhole edge may have become jagged or stepped because of the spread. Use a ruler to draw a smooth curve from the shoulder notch to the underarm, blending into the side seam. The side seam may have changed length slightly – compare it to the original side seam and adjust the hemline to match by measuring from the armhole notch down. Redraw the hemline if necessary, keeping it perpendicular to the grainline.
Step 5: Adjust the Shoulder Dart
The shoulder dart will also have opened. Redraw the dart legs so they meet at the original dart point (or at the bust point if the dart was rotated). The dart should be slightly wider now, which is correct – it provides the added fabric needed across the bust.
Your front bodice now has the correct fullness. Transfer the new pattern to a clean sheet of paper by tracing the adjusted lines. Mark all notches and grainline clearly.
Photo by Kelly Sikkema on Unsplash.
The Small Back Adjustment
A full bust adjustment often makes the back neckline and shoulders too wide because the front shoulder seam has moved outward. To fix this, you will reduce the back bodice width at the centre back, while keeping the armhole and neckline shape the same.
Step 1: Measure the Change
Lay the original back bodice piece beside the new front bodice, matching shoulder seams. Note how much longer the front shoulder seam has become – typically the same amount as the wedges you added. You need to remove that amount from the back shoulder area, not from the neckline.
Step 2: Draw Reduction Lines
On the back bodice, draw a vertical line from the centre of the shoulder seam (not the neck point) down to the armhole, about 2.5 cm (1 in) from the armhole edge. Stop at the armhole line and leave a hinge. Draw a second horizontal line from the shoulder seam to this vertical line, curving slightly to match the natural shoulder slope.
Step 3: Overlap and Tape
Cut along both lines, leaving the hinge at the armhole. Overlap the cut edges by the amount of length you need to reduce – the same amount you added to the front shoulder. Tape the overlap. This will bring the shoulder seam and neckline inward, narrowing the back.
Step 4: True the Seams
Redraw the shoulder seam so it matches the front shoulder length. Smooth the armhole curve if it became distorted. The centre back line remains unchanged; the neckline should not shift much, but if it did, blend it smoothly.
Finishing
Cut a test garment from muslin using your new front and back pattern pieces. Baste the shoulder seams, side seams, and waist dart. Try it on right side out, with the centre back pinned (or zipper basted if the pattern has a zipper). Evaluate the fit:
- The bust should have enough room without pulling across the front.
- The armhole should lie flat against the body, not gape.
- The back should be snug but not tight, and the neckline should sit smoothly.
- The shoulder seams should sit on top of your shoulder, not falling toward your neck or hanging over.
If the bust still feels tight, repeat the FBA with an additional 0.5 cm (¼ in) spread. If the back is too loose, overlap a little more. If the front shoulder seam is pulling toward the back, the small back adjustment was insufficient – increase the overlap slightly.
Photo by Christian Kaindl on Unsplash.
Mistakes to Avoid
- Cutting through the armhole hinge – The hinge is essential to keep the armhole shape intact. If you cut through, you will have to redraw the entire armhole, which is far more error-prone.
- Spreading too much at once – Add only the difference between your cup size and the pattern’s B cup. Adding extra “just in case” creates a baggy bodice that is harder to fix than a tight one.
- Ignoring the waist dart – The waist dart must be redrawn from the new spread. If you leave it as is, the fabric will not fall properly at the waist.
- Skipping the muslin test – Even if you measure precisely, paper adjustments can behave differently in fabric. A muslin test saves fabric and frustration.
- Forgetting to adjust the back – A full bust adjustment on its own can make the back shoulders droop. Always check the back shoulder length and perform the small back adjustment if needed.
With practice, these two adjustments become quick and intuitive. The result is a bodice that fits your body’s proportions, not a standardised set of measurements.