A centimeter is 10 millimeters, or approximately the width of a fingernail. Another way to imagine the size of a centimeter is in relation to inches. One centimeter is approximately three times smaller than an inch.
A centimeter is measured using the metric system, as opposed to the imperial or U.S. system of measurement. A ruler, the most common device used to measure distances, uses calibrated lines denominated into centimeters or inches, making it easy to compare between the two systems. It may also be helpful to determine the size of a centimeter in relation to common items. A more precise way is to use orders of magnitude, or the scale of relationships between numbers.