In order to convert inches to millimeters you have to use the formula I just provided below:
1 inch x (2. 54 cm/inch) x (10mm/1cm) = 25. 4mm
In other words, 1 inch equals 25. 4mm, 2 inches equals 50. 8mm, and so on. Make sure you simplify each part of the equasion (cross out like terms, etc. ).