The gram is a unit of mass (acceptable for use as weight on Earth) and is a multiple of an SI base unit with the symbol g.
Although without a prefix, it actually represents 1/1000 kg. It is the first subdivision of the SI base unit; kilogram and 100 g equals 3.527396195 ounces.
It is the most common unit for measuring ingredients (except liquid) in cooking and purchasing food goods in the world today.
The majority of nutritional values and information is expressed in terms of 'per 100g'.
1 g is roughly equal to the weight of bank note or a pinch of salt.
The milligram is a unit of mass (acceptable for use as weight on Earth) and is a submultiple of an SI base unit with the symbol mg.
1 milligram is equal to 0.001 g or 1/1000 g (one thousandth of a gram).
There exists 2 submultiples between mg and g - namely the decigram and the centigram but these are not commonly used in everyday life. The milligram is commonly used when expressing parts of a gram; especially in medicine applications.
A mosquito weighs about 2.5 mg, as does a grain of sand.