Convert the measurement into centimeters by multiplying by the appropriate conversion factor depending on the units of the initial measurements. For example to convert from inches to centimeters, multiply by 2.54. See the resources section for places you can find the appropriate values. If you are making the measurements yourself you can alternately use a ruler or measuring tape that allows you to measure directly in centimeters. If you already have your measurement in centimeters than you can skip this step.
Decide if centimeters are the best metric length unit to use. If the measurements are either very large or very small when expressed in centimeters, then it may be more appropriate to divide or multiply by factors of 10 to convert to a metric length unit such as meters, kilometers or nanometers that make the numbers easier to work with. See the resources section for a guide to the appropriate conversion factors.
Use centimeters to solve the problem just like you would inches, meters, miles or any other length unit. For example in a geometry problem you can use the Pythagorean Theorem with centimeters by inputting the two known side lengths into the equation in centimeters and the third unknown side will be solved for in centimeters.