Basic Units and Prefixes for Competitive Exams
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Units of measurement
Base units
The International System of Units (System International d ‘Unites’) is founded on seven base quantities, which are assumed to be mutually independent. These base units are:
Base quantity  SI hast unit  Symbol for unit 
Length  Metre 

Mass  Kilogram 

Time  Second 

Electric Current  Ampere 

Temperature  Kelvin 

Amount of substance  Mole 

Luminous intensity  Candela 

Prefixes
Prefixes are used to form decimal multiples and submultiples of Si units. The common prefixes are:
Factor  Prefix  Symbol 
 tera  T 
 giga  G 
 mega  M 
 kilo  k 
 hecto  h 
 deka  da 
 pico  p 
 nano  n 
 micro  μ 
 milli  m 
 centi  c 
 deci  d 
The symbol for a prefix is combined with the unit symbol to which it is attached to form a new unit symbol, e.g. kilometer (km), milligram (mg), microsecond (μs).