Waist 1. Button up the pair of jeans. Lay the jeans out on a flat surface with the top front edge of the waistband even with the top back edge and pull taut on the outside waistband corners. 2. Measure the top of the waistband from one side to the other. 3. Double this to get the jeans waist measurement.Inseam 1. Lay the jeans out on a flat surface. 2. Measure from the crotch seam to the outer edgeof the leg opening along the inseam of the leg.