created 30 January 2014
revised 4 February 2014
format corrected 2 April 2015

Pleat Math

To find out how much fabric you need for a pleated ruffle, count the layers:

If you fold under exactly as much as the spacing between pleats, so that the fold underneath exactly meets the fold on top, then the ruffle is three layers thick and you need three times as much fabric as the length of the finished ruffle.

If you fold under half an inch and space the pleats one inch apart, half the ruffle is three layers and half is one layer.  So you need twice as much fabric as the length of the ruffle: half, plus three halves.  (Another way to think of this is that you have, every inch, a half-inch tuck that takes up another inch.)

If you fold under twice the spacing, so that each underfold covers two pleats, it's five layers thick (three for the pleat, and two layers for the pleat on top of it), so you need five times the fabric.  (Another way to think of it: every inch you have a two-inch tuck that takes up four inches.)

If you fold under once and a half, half will be five layers and half will be three, so you need five halves plus three halves, which is four times the fabric.

When making a pleated skirt, I don't bother with math.  I cut a panel the desired width at the hem — usually all the fabric I've got, which is why my red-flowered skirt has black pockets — and place pins around the waist band to mark the desired number of pleats.  Then I divide the skirt into the same number of sections, pin the marks together, and form the pleats.  See 1950s Pleated and Gathered Skirts.

 

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