International System of Units (SI) - definition
International System of Units (SI) - definition
International System of Units (SI) is a standardized and globally adopted system of measurement units, developed to ensure consistency in scientific, technical, and commercial measurements worldwide. It was established in 1960 by the General Conference on Weights and Measures (CGPM) as a modern form of the metric system, based on seven base units from which all other derived units are defined. The SI system is administered by the International Bureau of Weights and Measures (BIPM), which is responsible for its development, standardization, and implementation.
The SI base units are: meter (length), kilogram (mass), second (time), ampere (electric current), kelvin (thermodynamic temperature), mole (amount of substance), and candela (luminous intensity). Each of these units is defined using invariant physical constants, such as the speed of light in vacuum, Planck’s constant, or Avogadro’s number, ensuring their precision and repeatability regardless of time or location.
The SI system forms the foundation of metrology—the science of measurement—and is used as the official system of units in most countries around the world. Its purpose is to eliminate ambiguity, simplify calculations, and facilitate the seamless exchange of measurement information and data across various fields of science, industry, and administration. Within the SI framework, decimal prefixes such as kilo-, mega-, milli-, and micro- are permitted to make it easier to express quantities with very large or very small values.
The modern approach to the SI system emphasizes full alignment with fundamental physics and the use of definitions based on natural constants, making it a universal measurement tool suitable for both laboratory conditions and everyday engineering or industrial practice. The unification of measurement units supports technological progress, global research collaboration, and the development of a knowledge-based economy.
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