Why do you multiply to convert centimeters to millimeters?

Take your number of centimeters and multiply that number by 10.

Because it's going to the right (the decimal point in the number which would have centimeters(cm) )

For example : If you were to be converting 12 cm into mm it would move the decimal point to the right once and it would be 120 mm and since it is a power of ten it would be cm x 10 = mm

Hope I helped!