Pleat Calculator — Box, Knife & Inverted Pleats

As a rule of thumb, box pleats use 3× the finished width and inverted pleats (a box pleat reversed) also use 3×, because each pleat hides two folds of fabric behind the visible panel. Spaced knife pleats use about 2×. These ratios assume the hidden fold depth is about half the visible pleat width — deeper folds use more fabric. The precise figure is: knife pleat fabric = number × (visible width + 2 × fold depth); box pleat = number × (visible width + 4 × fold depth).

A box pleat has two folds that face away from each other, creating a flat panel on the outside with the excess fabric hidden behind. It uses the most fabric but gives a crisp, structured look.

Common pleat widths are 2.5–5cm for skirts, 5–8cm for kilts, and 1–2cm for fine pleating. The pleat width is the visible width on the outside of the garment.

A kick pleat is not handled by this calculator. It is a single short vent at a hem or seam (typically a 15–23cm / 6–9in opening with a small underlap of about 4–6cm), so it adds a fixed amount of fabric for the underlay rather than multiplying the whole panel width. Allow extra for the underlay piece plus seam allowances, not a fullness ratio.