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In ancient times, each people had their own unit(s) of measurement, but with the development of trade, negotiations became increasingly difficult to carry out. The differences in measurements were a major obstacle for commerce to grow. At that point, the need for a standardization of measures arose.
Then, during the French Revolution, the French Academy of Sciences was tasked with creating a single system of measurement. Thus, the decimal metric system was born, which was later expanded and gave rise to the International System of Units (SI).

In the table below, you can find the main SI units:
 

Quantity	Name	Symbol
length	meter	m
area	square meter	m²
volume	cubic meter	m³
plane angle	radian	rad
time	second	s
frequency	hertz	Hz
speed	meter per second	m/s
acceleration	meter per second squared	m/s²
mass	kilogram	kg
density	kilogram per cubic meter	kg/m³
flow rate	cubic meter per second	m³/s
amount of substance	mole	mol
force	newton	N
pressure	pascal	Pa
work, energy, heat quantity	joule	J
power, energy flux	watt	W
electric current	ampere	A
electric charge	coulomb	C
electric voltage	volt	V
electrical resistance	ohm	Ω
conductance	siemens	S
capacitance	farad	F
Celsius temperature	degree Celsius	°C
thermodynamic temperature	kelvin	K
luminous intensity	candela	cd
luminous flux	lumen	lm
illuminance	lux	lx