Why Commercial Patterns Don't Fit
Commercial patterns are graded to a standard set of proportions that assumes a specific relationship between bust, waist, and hip measurements. For women with larger busts, the proportional difference between bust and waist is greater than the pattern's grading accounts for — resulting in garments that either fit the bust and bag elsewhere, or fit the waist and don't close across the bust. This isn't a fitting problem with your body; it's a drafting problem with the pattern.
The Full Bust Adjustment
The Full Bust Adjustment (FBA) is the standard technique for adding circumference to the bust of a fitted pattern without changing the rest of the garment. It involves slashing the pattern at specific points and spreading to add the required amount. The adjustment must be done at the correct location — cutting through the dart — otherwise the additional fabric creates construction problems rather than solving fit problems.
The amount to add: measure the difference between your full bust measurement and the pattern's bust measurement at the size you're cutting. This difference goes into the FBA. Add half the difference at the front bodice.
High Bust vs Full Bust
When choosing a pattern size, choose by your high bust measurement (measured under the armpits, above the fullest part of the chest) rather than your full bust. Then perform the FBA to add the required bust circumference. This produces a better starting point for the rest of the garment's fit than choosing by full bust and grading everything else down.
Getting Help
Pattern grading and fitting adjustments are among the most technically demanding aspects of garment construction. If you're struggling with fitting a specific garment, Heidi's project consultations address exactly this — bring the pattern, your measurements, and any mockups you've made.