Simple Coin Math - To convert millimeters to inches, divide the
number of millimeters by 25.4. Say you have a coin that is 38.1mm; 38.1 divided by 25.4
is 1.5 inches. To convert inches to millimeters, multiply the number of inches by 25.4.
So, if your coin is 1 1/2 inches in diameter: 1.5 times 25.4 is 38.1mm.