The metric system is a common nickname for the International System of Units, usually shortened to its French abbreviation, SI. SI is a kind of decimal system, meaning that the units increase and decrease by orders of ten. An example of a non-decimal system is a clock.
Basic SI Units
The entire SI system is based on seven units from which all others can be derived. These are temperature in Kelvin (K), time in seconds (s), distance in meters (m), mass in kilograms (kg), luminous intensity in candelas (cd), current in amperes (A) and amounts in moles (mol).
Increasing Orders of Magnitude
Being a decimal system, SI changes units by tens or thousands and indicates each change with a prefix. These are, from large to small: yotta (10^24), zetta (10^21), exa (10^18), peta (10^15), tera (10^12), giga (10^9), mega (10^6), kilo (10^3), hecto (10^2) and deca (10).
Note one of the seven basic SI units is a kilogram, which is 10^3 or 1,000 grams.
Decreasing Orders of Magnitude
Similarly, SI units also shrink by tens or thousands. These prefixes, from small to large, are: yocto (10^-24), zepto (10^-21), atto (10^-18), femto (10^-15), pico (10^-12), nano (10^-9), micro (10^-6), milli (10^-3), centi (10^2) and deci (10^-1).
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