How this calculator works
A pleated skirt is a wide rectangle gathered into the waist by folds. Each visible pleat takes its own width plus the fabric hidden in the fold. A knife pleat folds once in the same direction, so it uses one pleat depth. A box pleat has two folds facing out from a centre, so it uses two depths and roughly twice the hidden fabric. The number of pleats is the waist divided by the visible pleat width, rounded down so the skirt can close. The cut length is the skirt length plus the hem and the waistband depth.
Formula
pleats = waist / visible pleat width, rounded down. knife fabric width = pleats x (pleat width + pleat depth) + 2 x seam allowance. box fabric width = pleats x (pleat width + 2 x pleat depth) + 2 x seam allowance. cut length = skirt length + hem allowance + waistband depth.
Worked example
A 70 cm waist with 5 cm visible pleats fits 14 pleats. With 5 cm depth, knife pleats need 14 x 10 + 3 = 143 cm of width, while box pleats need 14 x 15 + 3 = 213 cm. A 60 cm skirt with a 4 cm hem and an 8 cm waistband is cut 72 cm long.
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Frequently asked questions
How deep should the pleats be?
Pleat depth is a design choice. Deep pleats give a fuller swing and use more fabric; 5 cm is a moderate depth for a school-style skirt. The depth must be at least as deep as the visible width if you want the pleats to hold a sharp fold.
Do I need to press the pleats?
Yes, and often. Press each fold before sewing and again after the waistband is attached. Wool and wool blends hold pleats well; cotton needs steam and may need edge stitching or a pleat-setting treatment.
How do I attach a pleated panel to a waistband?
Sew two rows of long stitches across the top of the pleated panel and draw them up until the top edge matches the waistband. Distribute the gathers evenly into the folds, then stitch the waistband to the right side, turn and finish.
What about the seam at the back?
The fabric width figure is the flat width before joining. Add a seam allowance for the centre back if you will insert a zip or sew the panel into a circle, and add a placket if the waistband overlaps.