What is a milligram?
A milligram is a unit of mass in the metric system, equal to one thousandth of a gram. It is commonly used to measure very small amounts of substances, such as medications or chemicals. For reference, a single grain of sand typically weighs around 50 milligrams.
What is a kilogram?
A kilogram is metric unit of weight subdivided into 1,000 grams. The base unit of mass in the International System of Units (SI) is a kilogram and not, as is quite often mistaken, the gram.
One liter of water weighs 1kg.