Metric SI units

The International System of Units is abbreviated “SI” from the French “le Système international d’unités”. SI is the modern form of the metric system and is a coherent and definable measurement system devised around multiples of ten. It is the planet’s most widely used system of measurement, both for everyday commerce and for engineering, science and technology.


Base SI units

Quantity Unit Symbol Equivalent Equivalent
Length metre m    
Mass kilogram kg    
Time second s    
Electric current ampere A C/s  
Absolute temperature kelvin K    
Amount of substance mole mol    
Luminous intensity candela cd    

Coherent derived SI units

Quantity Unit Symbol Equivalent Equivalent
Plane angle radian rad    
Solid angle steradian sr    
Frequency hertz Hz 1/s  
Force newton N kg m/s²  
Energy joule J Nm  
Power watt W J/s VA
Electric Charge coulomb C As  
Voltage – potential difference volt V W/A  
Electrical capacitance farad F C/V  
Electrical resistance ohm W V/A  
Magnetic flux weber Wb    
Magnetic flux density tesla T    
Inductance henry H    
Luminous Flux lumen lm    
Illumination lux lx lm/m²  

Further reading