The full bust adjustment, or FBA, is the most frequently needed alteration on commercial bodice patterns, because those patterns are typically drafted for a B cup. A fuller bust needs both more width and more length over the bust, plus a larger dart to absorb the added shaping, and an FBA delivers all three without distorting the neckline or armhole.
The technique rests on one idea: a fuller bust projects further, so the pattern must curve more over the apex. This means adding fabric in the bust region only, while keeping the shoulder, armhole and neckline unchanged. The classic slash-and-spread method does exactly that.
How to know you need an FBA
The clearest sign is when a bodice fits at the shoulders and neck but pulls across the bust, with diagonal drag lines running from the apex toward the armhole and side seam. The hem may also ride up at the front because length is being stolen to reach over the bust.
Comparing your full bust measurement to your high bust is the usual test. A difference of more than about 5 cm suggests the standard draft will be too small over the bust and an FBA is warranted.
Deciding how much to add
The total width to add is based on the gap between the pattern's drafted cup and your actual bust, distributed across the quarter pattern. A common approach adds roughly one to one and a half centimeters per cup size beyond a B, but measuring your own high-to-full bust difference is more reliable than any rule of thumb.
Remember that the amount you spread the pattern adds to both the width and the dart intake, so a larger FBA produces a noticeably deeper bust dart.
The slash-and-spread method step by step
- 1.Mark the bust apex, then draw a slash line from the hem up through the apex to the armhole notch.
- 2.Draw a second line from the apex out to the side seam, meeting the existing bust dart.
- 3.Cut along these lines, pivoting to spread the pattern open by the required amount at the bust.
- 4.Fill the opening with paper; the vertical spread adds width and the horizontal spread deepens the dart.
- 5.Add the small amount of length created at the hem, then true the side seam and hem level.
Pro tip
Keep the armhole and shoulder untouched by slashing only up to, not through, the armhole point. This is what preserves the sleeve fit while the bust grows.
Truing the dart and seams afterward
An FBA enlarges the bust dart, which must then be trued so its legs are equal and it points to, but stops short of, the apex. Fold the dart closed and redraw the side seam and cutting edge across it, so the sewn edge is smooth rather than stepped.
Check that the front side seam still matches the back side seam length after the adjustment. The FBA lengthens the front, so the back may need a matching adjustment or the excess eased in.
Redistributing the enlarged dart
- Keep it as a side bust dart for a classic, simple result.
- Rotate it into the waist for a cleaner side seam.
- Split it into two smaller darts to soften the shaping over a fuller bust.
- Convert it into a princess seam that routes the shaping invisibly through a style line.
Avoiding the adjustment altogether
Because the FBA exists to correct a standard B-cup draft, a pattern drafted to your own bust and high-bust measurements needs no FBA at all. Minerva Patterns supplies made-to-measure patterns in DXF AAMA, PLT and PDF built around individual measurements, so the bust room and dart are correct from the start. When you do work from standard patterns, though, the FBA remains an essential skill.
Frequently asked questions
How do I know if I need a full bust adjustment?
Compare your full bust to your high bust measurement. A difference over roughly 5 cm, combined with drag lines from the bust to the armhole on a muslin, indicates a standard B-cup draft is too small and needs an FBA.
Does a full bust adjustment change the armhole?
No, done correctly. You slash up to but not through the armhole point, so the shoulder, neckline and armhole stay the same while width and length are added over the bust only.
Why does the bust dart get bigger after an FBA?
Spreading the pattern to add bust projection opens both a width gap and a dart gap. The horizontal spread deepens the dart, which is the extra shaping a fuller bust needs.
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