Mcg to Mg Converter

Exactly 1000. The milligram (mg) is one-thousandth of a gram and the microgram (mcg, sometimes written ug for the Greek letter mu) is one-millionth of a gram, so 1 mg = 1000 mcg and 1 g = 1000 mg = 1,000,000 mcg. The relationship is exact by SI definition, no rounding involved. US drug labels use mcg rather than ug because handwritten ug on a chart can be misread as mg, which would multiply the dose 1000-fold. The ISMP and Joint Commission both recommend the spelled-out mcg for clinical use.

An IU (International Unit) measures biological activity rather than mass. The mass represented by one IU depends on the substance and sometimes its molecular form. IU remains common for vitamins A, D, and E and for some biologics, including insulin and heparin. Use a substance-specific conversion rather than treating IU as a universal mass unit.

For vitamin D (both D3 cholecalciferol and D2 ergocalciferol), 1 mcg equals exactly 40 IU. So a 25 mcg supplement is 1000 IU, a 50 mcg supplement is 2000 IU, and a 100 mcg supplement is 4000 IU (which is the US Tolerable Upper Intake Level for adults). Going the other way, divide IU by 40 to get mcg: 600 IU is 15 mcg (the RDA for adults under 70), 800 IU is 20 mcg (RDA for adults 70 and over), 2000 IU is 50 mcg. This converter applies the same factor for both D2 and D3 because the FDA treats them as equipotent on a mass basis.

Labels use micrograms when milligrams would require small decimals. IU measures biological activity and is not interchangeable with mcg or mg without a substance-specific factor. Vitamins A, D, and E have historically appeared in IU; follow the unit on the label rather than applying a generic conversion.

No. It converts units only. Supplement needs depend on age, diet, pregnancy, laboratory results, conditions, medications, and clinical guidance. Use the product label and ask a clinician about an appropriate amount.