Microgram

The microgram (symbol µg; sometimes written mcg or ug) is a unit of mass equal to one millionth of a gram: 1 µg = 10^-6 g. It is also equal to 0.001 milligrams and 0.000001 grams, with 1 µg corresponding to 1×10^-9 kilograms.

Micrograms are used to express very small masses and trace quantities in a variety of fields, including pharmacology, nutrition, toxicology, and environmental science. They are also common in expressing concentrations, such as micrograms per liter (µg/L) or micrograms per kilogram of body weight.

In nutrition and medicine, many micronutrients and drug doses are specified in micrograms per day. For example, the recommended daily intake of vitamin B12 for adults is about 2.4 µg.

Measuring microgram amounts requires high-precision instruments. Laboratories use analytical balances, as well as methods such as high-performance liquid chromatography (HPLC) and mass spectrometry, often after sample preparation to isolate the substance of interest.

Origin and standards: the term is formed from the SI prefix micro- (one millionth) and the gram. The microgram is a derived unit in the SI system; it is not a base unit. The symbol µ comes from the Greek letter mu; alternative spellings such as mcg or ug are common in various contexts, though each denotes the same microbiographic scale.