Lay the pants flat and smooth the waistband. Measure straight across from one side to the other. Multiply this number by 2 to get the full waist size. If the flat measurement is 17 inches, the waist size is 34 inches. If you are between sizes, choose the larger size for a better fit.
Take a point 3 inches above crotch (A) and mark the parallel point at both the side seams (B and C) to place the measuring tape. Measure across and double the number to find the measurement
Lay the trousers flat on a surface. Place the measuring tape at the top of the waistband and extend it straight down along the outer side seam to the bottom hem of the pants. The total measurement obtained represents the full length of the trousers.