Fabric width needed for a pleated panel.
Knife and box pleats typically need about 3\u00d7 the finished width in fabric.
A pleated panel needs much more fabric than its finished width, because the pleats fold the extra fabric underneath. The width of fabric needed is the finished flat width multiplied by the fullness. Knife pleats and box pleats generally need about three times the finished width, so a finished width of 20 inches requires about 60 inches of fabric.
Closer pleats use more fabric and give a crisper, fuller effect, and wider pleats use less. Check the pattern for the pleat size and spacing, and decide whether to use all the fullness at the top or to let the pleats fall to a fixed depth.
Mark the folds carefully with chalk or tailor tacks, fold and pin the pleats in place, and press them well before you stitch them down at the waist or the top edge. Stitching the pleats flat for the first few inches keeps them neat and helps them hang smoothly.
Choose fabric that takes a crease well, such as wool blends and crisp cotton. Fabrics that are very bulky or very slippery are harder to pleat, and a pleated piece should be sewn on a flat surface to keep the pleats lined up.