One gram contains 1,000 milligrams. A gram is the basic unit of mass in the metric system, also called the International System of Units. This system of measurement is used in most industrialized nations of the world, other than the United States.
Because the metric system is based on units of 10, it allows for easy conversion between units. Some of the common prefixes used include "milli-," meaning 1/1,000, "centi-," meaning 1/100, "deci-," meaning 1/10 and "kilo-," meaning thousand. One gram is also equal to 100 centigrams and 10 decigrams. One kilogram equals 1,000 grams. In the imperial system used in the United States, 1 ounce is the approximate equivalent of 28.35 grams.