§ Metric conversion table. Inches Millimeters(mm) 1/8 equals 3.2 1/4 equals 6.4 3/8 equals 9.5 1/2 equals 12.7 5/8 equals 15.9 3/4 equals 19.1 7/8 equals 22.2 1 equals 25.4 11/4 equals 31.8 11/2 equals 38.1 13/4 equals 44.5 2 equals 50.8 3 equals 76.2 4 equals 101.6