Question: how to calculate fabric for knife pleats?
Answer: So, to create a 1”pleat, you'll need 3” of fabric. For example, if your waist measurement is 25” and you want to create a fully pleated skirt, with 1”-wide pleats, you'll need to multiply the waist measurement by 3 and add seam allowances for each edge. 25 x 3 = 75 + 1 (2 x1/2” seam allowances) = 76.