To convert 400 micrograms (mcg) to milligrams (mg), divide the former by 1000; the result is 0.4 milligrams. Another way to convert micrograms to milligrams is to move the decimal point of the first quantity by three places to the left.
One microgram is equal to one-millionth of a gram, whereas 1 milligram equals one-thousandth of 1 gram. In comparison, 1 milligram equals 1,000 times 1 microgram. Both units are used in the field of medicine to administer drug dosage. Microgram's symbol is µg, but the abbreviation "mcg" is used in medicine so as to avoid confusion with milligram's symbol (mg).