# SI Base Units

The SI has seven base units for seven base quantities, which are assumed to be mutually independent. In addition to the meter, kilogram, and second for

(1) length, (2) mass, and (3) time, SI units include(4) electric current (charge/second) in amperes (A), (5) temperature in kelvins (K), (6) amount of substance in moles (mol), and (7) luminous intensity in candelas (cd).

The metric system involving the standard units of length, mass, and time, now incorporated into the SI, was once called the mks system (for meter-kilogram-second).

Another metric system that has been used in dealing with relatively small quantities is the cgs system (for centimeter-gram-second).