Systems of Units and Notations

Systems of Units

A measurement of any physical quantity must be expressed as a number followed by a unit. A unit is a standard by which a dimension can be expressed numerically. The units for the fundamental dimensions are called the fundamental or base units.

While carrying out calculations, there are several systems of base units that are available. However, the most common one is the International System of Units (also called SI, from the French "Système International des Unités") introduced by Griorgi in 1901, including the meter-kilogram-second-ampere (MKSA) subsystem representing the four fundamental dimensions length, mass, time, and electric current, respectively. The units for other dimensions are called secondary, or derived units and are based on the above fundamental units.

This portal employs the SI units that are commonly adhered to by virtually all-engineering professional societies.

  • The SI is the standard system used in today’s scientific literature.
  • The SI has seven base units, several derived units with special names, and many derived units with compound names.
  • In addition to the units, the SI system involves other recommendations, one of which is that multiple and submultiples of the MKSA units be set in steps of 103 or 10-3.

The fundamental SI units and abbreviations are listed in Table 1.

Table 1 The Seven Fundamental SI Units


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