a decimal system of weights and measures, adopted first in France but now widespread, universally used in science, mandatory for use for all purposes in a large number of countries, and favored for use in most (as in the U.S.). The basic units are the meter (39.37 inches) for length and the gram (15.432 grains) for mass or weight. Derived units are the liter (0.908 U.S. dry quart, or 1.0567 U.S. liquid quart) for capacity, being the volume of 1000 grams of water under specified conditions; the are (119.6 square yards) for area, being the area of a square 10 meters on a side; and the stere (35.315 cubic feet) for volume, being the volume of a cube 1 meter on a side, the term “stere,” however, usually being used only in measuring firewood. Names for units larger and smaller than these are formed from the above names by the use of the following prefixes: kilo-, 1000; hecto-, 100; deka-, 10; deci-, 0.1; centi-, 0.01; milli-, 0.001. To these are often added: tera-, one trillion; giga-, one billion; mega-, one million. With the addition of basic physical units it is now officially known by the French name Le Système International d'Unités (abbreviation SI) or in English as the International System of Units.
A decimal system of weights and measures based on the meter as a unit of length, the kilogram as a unit of mass, and the liter as a unit of volume. Compare US Customary System. See Table at measurement.
A system of measurement in which the basic units are the meter, the second, and the kilogram. In this system, the ratios between units of measurement are multiples of ten. For example, a kilogram is a thousand grams, and a centimeter is one-hundredth of a meter. Virtually all countries of the world, except the United States, use the metric system. Among scientists, the metric system is called SI — an abbreviation for Système internationale, which is French for “International System.”