Pant size 20 refers to 28 inches, which is equivalent to a waist circumference of 2 feet 4 inches. Pant size 83 refers to the waist circumference of 83 cm. Waist circumference of trousers: measured around the waist seam on both sides. It is recommended that the size of trousers be enlarged by two centimeters compared with the waistline of clean body when purchasing. This is related to size.