Metric system

The metric system is the common name for the Système International d'Unités or International System of Units. In scientific work, it is abbreviated SI. It is called the "metric system" because its units of length are based on the meter.

In 1878 the U. S. signed the treaty called the Convention du Mètre. Since then, both the metric system and the "U. S. Customary" system (miles, inches, pounds, etc.) have had legal status in the U. S. U. S. Customary units are in fact defined by reference to metric units; that is, legally, an inch is defined to be exactly 25.4 millimeters.

Common Prefixes Used in the Metric System

Prefix	Numerical Meaning
micro ($\mu$)	0.000001
milli (m)	0.001
centi (c)	0.01
deci (d)	0.1
deca (D)	10
hecta (H)	100
kilo (k)	1,000
Mega (M)	1,000,000