The metric system is the most widely used system around the world for measuring weight, distance and volume. Having a common system across all countries allows scientists to accurately compare their findings.
The metric system uses three basic units from which all others are calculated: grams for weight, meters for length and seconds for time. This gives all scientists the same standards of measurement when they conduct experiments.
To represent large amounts of a fundamental unit, prefixes are used to denote factors of 10. For example, a decameter is 10 meters, a hectameter is 100 meters and a kilometer is 1,000 meters. The use of factors of 10 to convert all units is much simpler for scientists because they just have to move the decimal place rather than divide by different numbers like three to get from yards to feet and 12 to get from feet to inches.
Gabriel Mouton first suggested a decimal-based measurement system in 1670 but it was not until 1790, during the French Revolution, when the current metric system was created. It was officially adopted by France in 1895 because it was much easier to use than the existing English system.
France made the use of the metric system mandatory in 1840 and by 1900 35 other countries had accepted the metric system as its standard unit of measurement. The United States is one of a handful of countries that have not officially adopted the metric system. Scientists use the system because it is universally recognized.
In 1960 the General Conference on Weights and Measures created a set of units that would compose the Systeme International d'Unite (SI Units) for use in scientific work. In addition to the kilogram, meter and second, the ampere was added to measure current, the kelvin to measure temperature, the mole to measure substance and the candela for luminosity.