Small Bust Adjustment
Excess fabric at the bust, or the pattern gaps away from your chest? If your full bust is less than 2 inches larger than your high bust (A cup or smaller), you need a Small Bust Adjustment. Enter your measurements and we'll calculate the overlap.
How the SBA works
Commercial patterns are drafted for a B cup (roughly 2 inches difference between high bust and full bust). If your difference is less than 2 inches — an AA or A cup — there is more fabric at the front bust than your body needs. The result: excess fabric that pools at the bust, a hemline that dips in front, or a dart that sits too high.
A Small Bust Adjustment removes this extra fabric using a slash-and-overlap technique — the inverse of an FBA. The same two cut lines are used, but instead of spreading the pattern open, you overlap the edges inward. The existing dart gets smaller to match. Pattern size is still determined by your high bust measurement.
How to take these measurements
High Bust
Wrap the tape directly under your armpits, above the bust. Parallel to the floor, snug but not tight. This sets your pattern size.
Full Bust
Wrap at the fullest part of your bust, parallel to the floor. For a small bust, the difference between these two measurements will be small — often less than 1 inch.
Do you actually need an SBA?
Subtract your high bust from your full bust. Patterns are drafted for a 2 in / 5 cm difference, so anything below that means there is more fabric in the front bodice than your body fills:
| Full bust minus high bust | Pattern cup | Typical SBA |
|---|---|---|
| 2 in / 5 cm | B — pattern default | None needed |
| 1 1/2 in / 4 cm | A/B | 1/4 in |
| 1 in / 2.5 cm | A | 1/2 in |
| 1/2 in / 1.5 cm or less | AA | 3/4 in or more |
The tell-tale signs are fabric that stands away from the chest above the bust, a wrinkle that folds down from the armhole, a side dart that points above where your bust actually is, or a front hemline that hangs longer than the back.
How to do a princess seam SBA, step by step
- Trace the center front and side front in your high bust size and mark the apex on the side front at the deepest point of the seam curve.
- Draw a vertical line on the side front, parallel to the grainline, from the hem through the apex to the armhole.
- Slash and overlap that line by the calculated amount, hinging at the armhole, and tape flat.
- Flatten the center front curve to match. On a small bust the princess seam should be noticeably straighter — that curve is what was creating the unfilled space.
- Shorten if needed. A smaller bust projects less, so it consumes less length. If the front bodice bagged vertically, remove a little length at the apex line as well.
- Walk the princess seam — the two seam lines should now match with only a small amount of ease through the bust.
- Level the hem and true the side seam against the back.
Common SBA mistakes
Sizing down instead of adjusting. Picking a smaller size to fix bust bagging shrinks the shoulders, armhole, and back too — parts that already fit. Size by high bust and take the excess out only where it exists.
Removing the dart entirely. Unless your measurement difference is essentially zero, you still need some shaping. A small dart is not a mistake to be eliminated; it is what keeps the bodice from hanging straight down from the chest.
Ignoring the hem. An SBA shortens the front at the center. Skipping the levelling step leaves the front hem visibly higher than the back.
Confusing an SBA with a narrow chest. Fabric pooling above the bust can also come from broad shoulders or a wide upper chest drafted into the pattern. If the excess is at the armhole rather than at the bust apex, an upper chest adjustment is the right fix.
Related tools
Excess fabric at the bust? Calculate the overlap amount for A cup and smaller.
Same FBA calculation for princess-seam patterns — spread the side front without darts.
Is your pattern too tight or too loose? Compare your body to the pattern to check ease by fit style.
Enter bust, waist, and hip — find your size across 11 brands with size charts. Sewing sizes ≠ store sizes.