What is the Full Bust Adjustment?
The Full Bust Adjustment (FBA) is a pattern modification that adds width and length to the front bodice of a sewing pattern to accommodate a larger-than-standard cup size. Commercial patterns are drafted to a B-cup. If your measurements give you a C-cup or larger, the FBA is necessary for any fitted bodice — without it, the front will pull, the side seams will angle forward, and the back neckline will lift.
How Much to Add
Calculate how much to add: measure your full bust, then measure your high bust (directly under your armpits, above the fullest point of the chest). Your pattern size should be chosen based on the high bust measurement. The difference between your full bust and your high bust tells you how much the pattern is short — subtract the pattern's cup allowance (typically 1 inch for a B-cup) from your difference. This is your FBA amount.
The Basic FBA Steps
- Trace your front bodice pattern piece.
- Mark the bust point (the fullest point of the chest when wearing your fitting undergarments).
- Draw a slash line from the bust point to the hem, parallel to the grainline.
- Draw a second slash line from the bust point out to the armhole seam, stopping 1–2mm before cutting through.
- Cut along both lines, leaving the armhole as a pivot point.
- Open the hem slash by the amount calculated (your FBA amount). This is the pivoting step — the pattern spreads at the hem while pivoting at the armhole.
- True the cutting lines — the side seam and center front now need to be redrawn as smooth curves.
- Redraw the dart to account for the new pattern shape.
After the FBA
The pattern will have a longer center front, a wider bustline, and a repositioned dart. The shoulder, neckline, and side seams above the bust should remain unchanged. Always make a toile (test version in cheap fabric) before cutting your fashion fabric — the FBA is a starting point, and fitting adjustments are normal.
The Princess Seam Version
For patterns with princess seams (vertical seams through the bust) rather than bust darts, the FBA process differs: you add width between the side front and center front panel at the bust point rather than making a slash-and-spread. The principle is the same — adding width at the fullest point — but the execution follows the seam lines.
Frequently Asked Questions
Only for fitted bodices and any garment that's structured at the bust. Loose garments, cloaks, a-line skirts, and similar pieces don't require an FBA.
It's a starting point, not a final measurement. Always make a toile and expect to make adjustments. The calculation gets you close; the fitting process gets you exact.
Yes — the FBA works on any bodice pattern regardless of whether it's a commercial sewing pattern or a cosplay-specific pattern. The modification is the same.