There are one million milligrams in a kilogram. A milligram is the smallest metric measurement and is equal to .001 of a gram. It takes 1,000 milligrams to equal 1 gram and 1,000 grams to equal a kilogram.
The milligram is a sub unit of a kilogram. The kilogram is the primary standard by which weight is calculated around the world. It is the base unit for the measurement of mass, and it was established in 1889 as being equal to one cubic decimeter of water. The first kilogram, from which all official kilogram weights are calibrated to, is kept at the International Bureau of Weights and Measures.