Before measuring:
1. Choose a clean, hard and flat surface at home, preferably a table.
2. Place a straight stretched measuring tool on the table.
Waist:
Take from the closet pants or jeans, that fit well both in length and width. Button the pants button and zip up the zipper, then shift the front of the pants about 10cm to the side
Firmly stretch the top edge of the pants waistband, read the waistband cm and multiply by 2 (video example results - 49cm x 2 = 98cm at the waist; corresponds to size W36)
Hips:
Place the tape measure so that it touches the ends of the side seams and the bottom curve end of the zipper's decorative seam (see image). Measure the hip width from one side of the fabric to the other (not to the seams)
(example results from the image - 56cm x 2 = 112cm at the hips)
Inseam (inner seam):
Outseam (outer seam):
Similarly, do the same and measure the outer side seams length of the pants (including the waistband).