If you are not using a pattern, this is my suggestion: Measure the size of the opening where you will sew the elastic (waist area, leg openings, etc.). Subtract 1” to that amount and presto! With this reduction and the overlap when you attach it, the elastic will fit properly, without too much gathering.

Cut the elastics in the corresponding lengths. Lap ends of elastic 1/2” (1.25 cm) and stitch securely. Divide elastic into quarters and mark. Do the same with the waist and leg openings. (FIG. 2)