Microgram

In the metric system, a microgram (µg; while the recommended symbol in the U.S. when communicating medical information is mcg) is a unit of mass equal to one billionth of a kilogram, one millionth of a gram, or one thousandth of a milligram. The unit symbol is µg according to the International System of Units. In µg the prefix symbol for micro- is the Greek letter µ (Mu).