micrograms

Microgram (symbol µg or mcg) is a unit of mass in the metric system equal to one millionth of a gram (10⁻⁶ g). It is also equal to one thousandth of a milligram. Because the micro- prefix denotes a factor of 10⁻⁶, the microgram is used for very small quantities in science and medicine.

Common relationships with other units are: 1 milligram (mg) equals 1000 micrograms, and 1 gram (g) equals 1,000,000 micrograms. A microgram is also equal to 1000 nanograms (ng).

Micrograms are widely used to quantify trace amounts of substances in nutrition, pharmacology, toxicology, and environmental science. Nutritional labeling often expresses vitamins and minerals in micrograms, for example B vitamins or folate, while toxicology and exposure assessments report small concentrations in µg for substances encountered at low levels.

Measuring microgram masses requires precise equipment, such as analytical balances, gravimetric methods, or spectrometric techniques when dealing with solutions. In liquids, concentrations are sometimes reported as micrograms per liter (µg/L) or per kilogram (µg/kg).

Note that the µg symbol may also be written as mcg in older texts or on some labels. The term microgram describes mass, not volume, and its use is most common where quantities are too small to express conveniently in milligrams.

Related concepts include the micro- prefix, nanogram (ng), and milligram (mg).