Centimeters to millimeters (cm to mm)

One centimeter is exactly 10 millimeters. That is the meaning of the metric prefixes, not a measurement: milli is a thousandth, centi a hundredth and kilo a thousand, so every conversion inside the metric system is a power of ten and nothing has to be looked up.

Worked through: 10 cm x 10 = 100 mm.

Going the other way, one millimeter is 0.1 centimeters.

To convert without a calculator, multiply by 10. Rounding that to 10 is within 0% for most purposes.

A pure decimal shift: one centimeter is ten millimeters by definition, both being powers of ten from the meter. There is no conversion factor to remember, only a decimal point to move.

Precision is worth matching to the input. A measurement given as 1 cm carries one or two significant figures, and reporting its conversion to six implies a precision the original never had.