200 milligrams is equivalent to 0.2 gram. Milligram is a measurement of mass or weight in the metric system equal to 1/1000 of a gram. Milligram is also spelt "Milligramme," particularly in British English.
The abbreviation of milligram is mg. "Milli" is one of the 20 prefixes in the International System of Units, and its factor is 0.001. A gram is a metric unit equal to 1/1000 of a kilogram. It is equal to the mass of 1/1000 of a liter of water at 4 degrees Celsius. Milligram originates from the French "milligramme" from the early part of the 19th century.