§ Metric conversion table. Inches Millimeters (mm) 1/4 equals 6.4 5/16 equals 7.9 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 23/16 equals 55.6 24/16 equals 57.2 27/16 equals 61.9 28/16 equals 63.5 29/16 equals 65.1 211/16 equals 68.3 212/16 equals 69.9 215/16 equals 74.6 31/16 equals 77.8 33/16 equals 81.0 35/16 equals 84.1 37/16 equals 87.3 39/16 equals 90.5 313/16 equals 96.8