What does microgram mean?
A microgram is an extremely small metric unit of mass, equal to one millionth of a gram. The abbreviation μg, sometimes written as ug in plain text, is widely used in science, medicine, and environmental analysis. Because a microgram is one thousandth of a milligram, it is especially useful for describing very small quantities of substances such as hormones, proteins, contaminants, and pharmaceutical compounds. The word is formed from the combining form micro-, meaning “small,” and gram, a metric unit originally derived from the Greek word for letter and, through its history as a unit of weight, “a small weight.” A microgram should not be confused with a milligram: the former is one thousand times smaller. In everyday conversation, micrograms usually appear in technical or scientific discussions rather than ordinary measurements.
nounA unit of mass equal to one millionth of a gram, or 0.000001 gram. It is used for quantities too small to be conveniently measured in milligrams or larger units.
- A metric unit of mass equal to one millionth of a gram.
"The sample contained only a few micrograms of the substance."
"Each vial contained less than one microgram of the purified compound."
"The researchers detected trace amounts of the contaminant, measured in micrograms."
The plural is micrograms when referring to multiple units or separate measured quantities.
"The samples contained only a few micrograms of DNA."
A microgram is the tiny mass of a speck of dust, yet it can be enough to reveal what is inside a sample.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does microgram come from?
Microgram combines the international scientific prefix micro-, meaning “one millionth,” with gram, the metric unit of mass. The prefix micro- comes from Greek mikros, meaning “small,” while gram ultimately derives from Greek gramma, a small unit of weight. Together, the elements express a unit equal to one millionth of a gram.
Related word forms
How microgram is actually used
The spelling microgram is standard in British and US usage; microgramme is also accepted in British English. The term is common in scientific, pharmaceutical, and forensic contexts.
Easily confused with microgram
A microgram is one thousandth of a milligram, while a milligram is one thousandth of a gram.