Measurement Units

An evocative representation of the seven base units of the International System
INRIM is responsible for realising the national reference standards of the measurement units of the International System

As a national metrology institute (NMI), INRIM is responsible for realising, maintaining and developing the reference standards of the measurement units of the International System (SI).

The mere existence of such reference standards guarantees the traceability of every measurement to the SI, meaning the reliability of the measurements and their comparability at international level.

The SI is a language shared by all the countries parties to the Metre Convention, a treaty signed in Paris in 1875.

From 1971, it includes 7 base quantities and their corresponding 7 base units of measurement:

 base quantities  base units     
 length  metre
 mass  kilogram
 time  second
 electric current  ampere
 thermodynamic temperature      kelvin
 amount of substance  mole
 luminous intensity  candela








In 1875, the measurement system included only the three base units metre, kilogram, and second for, respectively, the quantities length, mass, and time.

At first, the base unit for the temperature was the degree Centigrade, renamed degree Celsius afterwards.

The SI is constantly evolving. Current developments consist in the attempt to redefine the reference standards of measurement units in terms of fundamental physical constants.

This approach would enable to realise more accurate and stable reference standards.

INRIM is contributing to the redefinition of the kilogram, the kelvin, and the ampere. Further research to realise the candela through the counting of photons are also under way.


Last modified: 04/20/2018 - 17:22