The first number in pants size is the waist: More specifically, the size of the waist measured by circumference in inches. Waist size is usually indicated with a W. For pants labeled with a waist measurement of 25, this means a pair of pants with the smallest of common waistband widths, namely, 25 inches. This extremely narrow waistband width shows up especially in women’s jeans, but can also be found among jeans for boys. Waist sizes in men’s pants generally range from W 28 to W 40.
The second number in pants is length: The leg length is also indicated in inches and is marked with an L. As in classic clothing sizes, the inner seam, or distance from crotch to floor, is measured. In principle, the length of men’s and women’s pants are no different and common sizes typically range from a length of 30 inches (L 30) to 36 inches, or L 36. Since these sizes are issued in 2-inch increments, some individual manufacturers produce pants in the intervening, odd-numbered, or intermediate, leg lengths.
If you want to convert the size to the metric system, you must use factor 2.54, because an inch is equal to 2.54 centimeters. Therefore, a pair of pants with a length of 32 inches has a leg length of 81 centimeters.