The International System of Units (SI) provides the basis to which we measure the world around us, and ensures that measurements made anywhere in the world are comparable. The SI system is the basis of commerce, allowing goods to be valued and exchanged with confidence and to support every aspect of scientific research.

On November 16, 2018, the unanimous historic vote of the Member States and Associate Members at the 26th General Conference on Weights and Measures (CGPM) approved the upgrading of the International System of Units, that is, the redefinition of the SI system, which dates back to 1960 and represents an international an agreed basis for demonstrating measurements at all levels of accuracy and in all fields of science, technology and human action. The revised SI lists new definitions of four basic units: kilogram, ampere, kelvin and mole, which are based on the determined values of four natural constants: Planck constant (h), elemental charge (s), Boltzmann constant (k) and Avogadro number (N_A) respectively. The redefinition of the four basic units at the same time is unprecedented and requires simultaneous global cooperation in different metrology fields.

The definitions of all seven SI units since May 20, 2019, when the new definitions for kg, ampere, kelvin and mole came into force, have been uniquely expressed through the explicit formulations of constants, and specific mises en pratique have been established so to explain the implementation of the definition of each of the basic units in practice. Redefinition of the SI system establishes a set of seven fundamental constants, known as the "defining constants of the SI system":

Legal units of measurement in Bosnia and Herzegovina are established by the SI system of units.

The Law on Units of Measurement ("Official Gazette of BiH", No. 19/01) is in force, and changes are expected with respect to the changes defined for the four basic units of measure kg, A, K and mole from May 20, 2019.

International Vocabulary of Metrology – Basic and general concepts and associated terms (VIM) JCGM 200:2012 (3rd edition) - https://www.bipm.org/en/publications/guides/vim.html

Measurement unit is a real scalar quantity, defined and adopted by Convention, with which any other quantity of the same kind can be compared to express the ratio of the two quantities as a number.

Measurement standard (etalon) is realization of the definition of a given quantity, with stated quantity value and associated measurement uncertainty, used as a reference.

Metrological traceability (traceability) is property of a measurement result whereby the result can be related to a reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty.

Calibration is an operation that, under specified conditions, in a first step, establishes a relation between the quantity values with measurement uncertainties provided by measurement standards and corresponding indications with associated measurement uncertainties and, in a second step, uses this information to establish a relation for obtaining a measurement result from an indication.