What is 31 inches to millimeters? The answer is that 31 inches equals 787.4 millimeters.
How to convert 31 inches to mm? We know that one inch is equal to 25.4 millimeters, so to convert 31 inches to millimeters, we must multiply the amount of centimeters by 25.4, which means that 31 inches is equal to 31 inches × 25.4 = 787.4 mm.
See also: How to convert 31 mm to inches.