The SI units
The International System of Units (SI) is a globally agreed system of measurements that was formalised in 1960. There are seven base units, which make up the SI, and guide the measurement of quantities like physical size, temperature and time.
Kilogram (kg)

Unit of measurement of mass 
Metre (m)

Unit of measurement of length 
Second (s)

Unit of measurement of time 
Ampere (A)

Unit of measurement of electric current 
Kelvin (K)

Unit of measurement of thermodynamic temperature 
Mole (mol)

Unit of measurement of amount of substance 
Candela (cd)

Unit of measurement of luminous intensity 
This International System of Units is necessary to ensure that our everyday concepts of measurement, whether a metre or a second, remain comparable and consistent worldwide. Standardising measurements ensures society has confidence in information. For instance, the kilogram is used every day, and defining this quantity means that consumers can trust that the shop is really providing the amount they say they are. Having reliable information on issues such as climate change, pollutions and medical diagnostics is important to society. Reliable measurement allows effective decisions to be made.
See what the expected redefinition in 2018 will mean for the SI units
Using the SI units
Learn more about the SI units and how to apply them
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