A microgram is a unit of mass equal to one-millionth of a gram. It is commonly used in scientific fields, particularly in chemistry and biology, to measure very small quantities of substances. For context, there are 1,000 micrograms in a milligram and 1,000,000 micrograms in a gram. Micrograms are often used in medical dosages, such as in the measurement of vitamins or medications. For example, the recommended daily intake of Vitamin B12 is often expressed in micrograms. This precise measurement helps ensure that individuals receive the correct amount of essential nutrients or medications.