The International System of Units, known by the international abbreviation SI, is the modern form of the metric system. It is the only system of units in which all seven base units are defined by international agreement. The SI was first published in 1960 and has been revised several times since then. The most recent revision was published in 2019.

The SI defines seven base units: the meter (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol), and candela (cd). These units are used to define all other units in the SI. For example, the unit of force is derived from Newton’s second law of motion: F = (ma), where F is force, (m is mass), and (a is acceleration). One Newton equals one-kilogram meter per second squared—that is, N = kg · m/s2. Similarly, the unit of electric charge is derived from Coulomb’s law: Q = I · t, where Q represents charge (in coulombs), I denotes current (in amperes), and t stands for time (in seconds).

Because it relies on fundamental physical constants rather than arbitrary standards like those that defined earlier systems of measurement, the SI provides a more precise and consistent way to measure quantities than any previous system. In addition, because it uses standardized prefixes that indicate multiplication factors — such as kilo- or mega, and the (SI) facilitates communication about measurements across language barriers. As a result, scientists work around utilizing a common set of measurements to promote collaboration and progress in technological innovation.