Pleat Calculator
Every pleat folds extra fabric back into the finished width — how much extra depends on the pleat style.
Knife pleats vs. box pleats
A knife pleat folds in one direction only, so each pleat uses about twice its visible depth in extra fabric. A box pleat folds toward the center from both sides, meeting in the middle — that doubles the fabric consumption again, to roughly four times the visible depth per pleat, for the same finished look.
Keeping pleats even
Divide your finished width by the number of pleats to get the spacing between pleat centers, then mark every fold line before you start pinning — pleats that are marked out in advance stay far more even than ones folded by eye as you go.
Pressing sets a pleat, stitching holds it
A hot press along each fold is what gives a pleat its crisp edge. Edgestitching or understitching the top few inches of each pleat keeps it from working loose during wear or washing, especially on a waistband or skirt.