Conversion of Centimeters to Inches

Use a centimeter, 1/100 of a meter, to measure lengths in the metric system. The metric system is a decimal-based system, working in multiples of 10. "The United States is now the only industrialized country in the world that does not use the metric system as its predominant system of measurement," according to the National Institute of Standards and Technology (NIST), making the ability to perform conversions more important than ever to daily life.

Estimated Conversion

Estimate a conversion by multiplying the number of centimeters by 0.4 to obtain an approximate value. Multiply 20 centimeters (20 cm) by 0.4 and the estimated value is 8.0 inches. Remember this is an estimate, but acceptable for small amounts.

Precise Conversion

Perform a precise conversion by multiplying the number of centimeters by the more accurate value of 0.3937008 for the length in inches. (Some sources use 0.393700787 for even greater precision--see Resource 2) Thus, 20 centimeters multiplied by 0.3937008 = 7.9 inches, only .1 inches different from the estimated value.

Comparison

Consider a larger distance. Covert 592 centimeters to inch measurement. Using the approximate value of 0.4 in/cm, the conversion would be 236.8 inches. The more precise conversion is 592 centimeters multiplied by 0.3937008, equaling 233.1 inches, or more than 3.5 inches off of the estimate value.

How to Choose

Estimate when taking a test and selecting from multiple choice answers. Eliminate blatantly erroneous answers quickly. Choose the specific measurement when working a problem from scratch for the solution.

Reverse the Process

Reverse the conversion, changing inches to centimeters, by using a value of 2.54 centimeters per inch. Multiply the number of inches by 2.54 to determine the number of centimeters. Use 2.5 as the estimated value.

Tools

Conversion charts and tools are widely available on the Internet. NIST supplies length, area, weight, volume and temperature estimate conversions on their website, as well as a variety of educational resources for all things metric (Resource 1). Access a conversion tool using the specific values at Resource 3, a site that also provides exercises in conversion.