Microgram (mcg)
Definition
One millionth of a gram (10⁻⁹ kg), written mcg in medicine.
History
The microgram is one millionth of a gram, a thousandth of a milligram. In medicine it is written mcg rather than µg to avoid a handwritten mix-up with mg.
Where it is used
Micrograms measure very small doses of vitamins and drugs, such as vitamin D, folic acid and thyroid medication.
Typical uses include vitamin and drug doses.
Conversion pages
These pages convert microgram to or from another unit in weight.
No conversion pages use this unit yet.
Other Weight units
Sources
- BIPM SI BIPM, The International System of Units (SI), 9th ed. (2019) · Dataset reviewed Nov 11, 2026