Zipper fly builder
Start with a garment preset, then match the usable zipper chain and the tested front pattern. Dimensions refer to finished construction lines; the selected allowance is added to the fabric pieces.
Before generating
Use the notes below to understand which measurements shape the draft, which options change construction, and what should be measured again when values conflict. Presets are starting points; the submitted values drive the result.
Enter the usable chain length, not the full tape. The top stop normally sits below the waist seam so it can be enclosed without bulk. The bottom stop must remain above the tight crotch curve, leaving room for the facing and shield to turn.
Overlap width hides the zipper but must not add garment circumference. When closed, the left and right center-front seam lines still meet. Any extension projects beyond that line and belongs to the closure construction rather than the finished body width.
Facing width must exceed both the overlap and the topstitch offset. A facing that ends beneath the decorative line creates a ridge and cannot support the lower curve. The generator rejects combinations that leave less than 5 mm of internal coverage.