A centigram is a unit of measurement in the metric and International System of units (SI) and is equivalent to one hundredth of a gram. It is a seldom used unit as the gram and milligram are much more common. Its primary use is in the laboratory, for precise measurements of mass.
The SI system is derived from a version of the metric system, and the basic units and conversions are the same in both systems as is a centigram. A gram is one thousandth of a kilogram, which is defined as the mass of a standard prototype mass as agreed upon by international convention. This mass was previously held to be equal to the mass of 1 cubic decimeter of water, a cube with sides of 10 centimeters (3.937 inches) in length. A centigram, therefore is 0.00001 of a kilogram or 1 x 10^{-5} kilograms.
The term centigram is constructed by combining the base term "gram" with the prefix "centi-," which means "one hundredth of." While the kilogram is the base unit of mass for the SI system, it is derived from the gram, and the term is constructed by adding the prefix "kilo-", meaning 1,000, to the base "gram." All units of mass in the SI system are constructed in a similar fashion, by adding the appropriate prefix to the base of "gram."
Units of mass, linear distance, and volume are directly related in the SI system. One gram of water has a volume of 1 milliliter and fills a cube 1 centimeter on a side. This relationship allows for the quick conversion of units of mass and volume of water. For example, a centigram of water, as one hundredth of a gram, must necessarily have a volume of one hundredth of a milliliter.
As a unit of mass, a centigram is most often encountered when using a type of scale, or balance, called a centigram balance. This type of balance is so named because it is capable of measuring the mass of an object to the nearest 0.01 gram, or centigram. A centigram balance, or scale, might be found in a laboratory or kitchen and might be used for measuring quantities of dry chemicals for experiments or small amounts of food.