Pleated Skirt Calculator (fabric width for knife & box pleats)

Understanding the pleated skirt calculator — concept and principle

This calculator works out how wide a strip of fabric to pleat for a straight pleated skirt, the visible pleat spacing, the cut length and how much fabric to buy. It handles knife and box pleats and is used for school uniforms, kilts-style skirts and costume making.

Each pleat hides fabric: with the default inputs the result is 195 cm flat width (2.71 × waist · 1.21 m fabric).

How it is calculated

Waist with ease W = waist + ease.
Fabric hidden by each pleat: knife pleat 2 × depth; box pleat 4 × depth.
Flat width = W + pleats × take-up + 2 × closing seam allowance.
Visible spacing = W ÷ number of pleats.
Cut length = skirt length + hem + waist seam allowance.
Panels = ⌈(width − 2 × seam) ÷ (fabric width − 2 × seam)⌉; fabric to buy = panels × cut length.

The principle

A pleat folds fabric back on itself, so part of the width is hidden behind the visible surface. A knife pleat of depth d folds under by d and back by d, hiding 2d. A box pleat is two knife pleats facing away from each other and hides 4d. The visible width at the waist stays the waist plus ease, and the hidden fabric is added on top. When the knife-pleat depth equals the visible spacing, the flat width is about three times the waist, the classic rule of thumb. Wide skirts need several panels joined so each seam hides inside a fold.

Worked example

Default inputs: waist 70 cm, ease 2 cm, 20 knife pleats 3 cm deep, length 55 cm, hem 4 cm, waist seam 1.5 cm, closing seam 1.5 cm, fabric 150 cm wide.

W = 70 + 2 = 72 cm; take-up per pleat = 2 × 3 = 6 cm.
Flat width = 72 + 20 × 6 + 3 = 195 cm, which is 2.71× the waist.
Visible spacing = 72 ÷ 20 = 3.6 cm.
Cut length = 55 + 4 + 1.5 = 60.5 cm.
Panels = ⌈192 ÷ 147⌉ = 2; fabric = 2 × 60.5 = 1.21 m.

Each point is the calculator re-run with only “Number of pleats” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Number of pleats	Fabric width to pleat (cm)
5	105
10	135
15	165
20	195
25	225
30	255
40	315

How to read the result

Mark pleat lines carefully on the flat fabric before folding, and baste them in place before attaching the waistband. Check that joins fall inside the folds. This is a straight rectangular skirt; one that flares towards the hem needs a shaped pattern.

Common mistakes

Forgetting the ease, which makes the waistband too tight.
Using box-pleat depth in a knife-pleat calculation.
Cutting panels without seam allowances.
Using fabric that will not hold a crease.

Keep in mind: Fabric shrinks and pleats relax with washing. Pre-wash the fabric and check the care instructions before cutting.

Frequently asked questions

How much fabric do I need for a pleated skirt?

Roughly waist plus pleat take-up; for 20 knife pleats 3 cm deep on a 72 cm waist, about 195 cm of width.

How much fabric does a box pleat use?

Four times its depth, twice as much as a knife pleat of the same depth.

Why is "three times the waist" a common rule?

Knife pleats whose depth equals the visible spacing need about three times the waist width.

Sources: Geometry of knife and box pleats (each fold hides fabric equal to the fold depth), as used in standard dressmaking pattern drafting

Checked 9 Nov 2026. Geometry of knife and box pleats (each fold doubles the hidden fabric); ease and allowances are example values you can change.

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