despite what you thought, you WILL need your math skills at this time in life...

so, think back to 7th grade with geometry and algebra and warm up those math muscles.

pleats are a matter of preference for the garment design AND the specific fabric you chose. Some fabrics are perfect for knife pleats, some fabrics won't fold too small, some fabrics sag when you fold them too big...

so... determine what your preference of pleat size is for the garment you designed. then try to fold your fabric in that pleat size (just thumb it over and hold down iwth a book, don't iron it yet!) and make modifications/compromises until you have what you want. if you haven't picked out your fabric yet, try the size you want on the various fabrics you are choosing from (just fold it over in the store in a rough estimate).

NOW comes the calculations. If you were making a skirt, for example, and you want your pleats to be 1/2" and double back on themselves (accordian pleats) and your waist is 27", now calculate: it takes 1" for each pleat (1/2" doubled back = 1") so the answer is, will need 54" of fabric, plus 5/8" x2 for the seam/zipper installation.

if you wanted, say 1/2" pleat but and extra 1/2" between each pleat, then that is 1.5" inches for each pleat (1/2" pleat doubled back = 1" plus the 1/2" between each pleat). The answer is, 37" waist times 1.5" = 40.5" plus 5/8" x2. (er, in general that design might work best with 5/8" pleat and 3/8" between each pleat)

to make the pleats: determine the size of your pleat (perhaps 1/2" for accordian pleats) and make a cardboard template that is 1/2"... tuck it into your fabric and press against it. repeat for each pleat until the full width of the fabric is done.

OR to do this WITHOUT math try this:

determine your pleat preference and your fabric capabilities. Then, using the raw yardage, just press it out until you have the width of fabric that you need pleated. I recommend basting it down while it is still on the ironing board, and then you can work with it to style your garmetn.