International System of Units

Like all metric systems, the SI uses metric prefixes to systematically construct, for the same physical quantity, a set of units that are decimal multiples of each other over a wide range.

The International System was published in 1960, based on the MKS units, as a result of an initiative that began in 1948.

matters related to the development of the International System of Units (SI), preparation of successive editions of the SI brochure, and advice to the CIPM on matters concerning units of measurement.

The SI base units are the building blocks of the system and all the other units are derived from them.

Arrangement of the principal measurements in physics based on the mathematical manipulation of length, time, and mass.

These units are used in combination with SI units in common units such as the kilowatt-hour (1 kW⋅h = 3.6 MJ).

The units and unit magnitudes of the metric system which became the SI were improvised piecemeal from everyday physical quantities starting in the mid-18th century. Only later were they moulded into an orthogonal coherent decimal system of measurement.

Closeup of the National Prototype Metre, serial number 27, allocated to the United States