A full bust adjustment (FBA) adds width and length over the bust to a pattern chosen by your high bust, and makes the bust dart bigger, so the shoulders, neckline and armholes fit while the front covers your bust without pulling. You usually need one when your full bust is more than about 5 cm (2 in) larger than your high bust, because most commercial patterns are drafted for that difference, often described as a B cup. You can skip it on close-fitting knits, loose and oversized designs, gathered or elastic bodices, and patterns drafted from your own bust measurements.
What does a full bust adjustment do?
A pattern chosen by full bust fits the bust but is too big everywhere else on a fuller-busted body: the shoulders slide, the neckline gapes and the armholes are too deep. A pattern chosen by high bust fits the frame but is too small over the bust. A full bust adjustment combines the two: the frame of the smaller size, with extra room where the bust needs it and a dart that shapes it.
How do I know if I need an FBA?
Take two measurements, standing relaxed, in the bra you will wear:
- High bust: around the chest high under the arms, above the bust at the front and across the shoulder blades at the back.
- Full bust: around the fullest part of the bust, tape level.
| Full bust minus high bust | What to do on most commercial patterns |
|---|---|
| 5 cm (2 in) or less | Choose the size by full bust: no FBA |
| More than 5 cm (2 in) | Choose the size whose bust is about your high bust plus 5 cm (2 in), then do an FBA for the rest |
Some independent pattern companies draft for a C or D cup instead; their size chart or instructions say so.
In a toile or a finished garment, the signs are recognizable:
- Drag lines from the bust toward the armholes.
- A front hem that rides up higher than the back.
- Side seams pulled forward.
- A button front that gapes between buttons.
- Gaping armholes and a loose neckline, if you chose the size by full bust.
How much do I need to add?
Compare your full bust with the bust measurement of the size you chose by high bust, on the body measurement chart (not the finished garment measurements). The difference is the total to add. A front pattern piece is half of the front, so spread each side by half the difference.
Example: high bust 92 cm (36 in), full bust 102 cm (40 in). The difference is 10 cm (4 in), so you choose the size with a 97 cm (38 in) bust, about your high bust plus 5 cm. You need 102 minus 97, so 5 cm (2 in) more in total: spread the front piece by 2.5 cm (1 in).
How is a full bust adjustment done?
The classic method on a front with a side bust dart, often called the Y method:
- Mark the bust point on the pattern: about 2 to 3 cm (1 in) beyond the tip of the bust dart, or measured from your own bust height and bust span.
- Draw three lines: from the hem straight up to the bust point, parallel to the grainline; from the bust point to the armhole, about a third of the way up from the side seam; and through the middle of the side dart to the bust point.
- Cut from the hem up the first line and on to the armhole, stopping a hair short of the armhole seam line to leave a paper hinge. Cut along the dart line to the bust point, again leaving a hinge.
- Spread the side section outward by the amount you calculated, keeping the two vertical cut edges parallel. The side dart opens wider by itself.
- Lengthen the center front. The side section now hangs lower than the center front. Cut across the center front section horizontally, below the bust, and lower its bottom part until the hems line up.
- Tape paper behind, redraw the dart with its tip 2 to 3 cm (about 1 in) short of the bust point, and true the side seam and hem.
The front is now wider and longer only over the bust, with a bigger dart, while the shoulders, neckline and armhole are unchanged. Practice on a copy of the pattern and check the result with a toile.
A dart that grows past about 7 to 8 cm (3 in) of intake is easier to sew and looks better split in two (a side dart and a waist dart) or moved into a princess seam. See how to sew darts for sewing them flat.
When can I skip the FBA?
- Knits with zero or negative ease. A close-fitting jersey top stretches over the bust. A difference of up to about 7.5 cm (3 in) is usually absorbed; beyond that, add a little length at the center front so the hem stays level.
- Loose and oversized designs. With 20 cm (8 in) or more of ease at the bust, a boxy top or a kimono jacket already has the room. Check the front length, though.
- Gathered, smocked or elastic bodices, wrap tops and drawstring necklines, where the fullness adjusts itself.
- Patterns drafted from your measurements. A made-to-measure draft starts from your own bust, so there is nothing to adjust afterward.
That last case is how Sewly works. Its woven bodices, in the woven top, the shift dress and the fit-and-flare dress, are drafted from your bust, underbust, bust height and bust span: the side bust dart's intake comes from the difference between your bust and underbust, the bust point is placed from your bust height and span, and the center front gets a little extra length to go over the bust. A toile is still wise, especially with a very full bust, but there is no FBA to draw on paper. More in custom-fit sewing patterns.
What about a small bust adjustment?
A small bust adjustment (SBA) is the reverse: the same cuts, but you overlap the pieces instead of spreading them, which removes width and length over the bust and makes the dart smaller. You need it when a pattern chosen by your frame shows loose, empty folds pointing at the bust, or a dart that ends in a bubble.