Medication Unit Converter

A microgram (mcg or ug) is one millionth of a gram, or one thousandth of a milligram. It is the smallest standard unit used in medication dosing. Common medications measured in mcg include levothyroxine (25-200 mcg), folic acid (400-800 mcg), and vitamin B12 (1,000 mcg).

There are exactly 1,000 micrograms (mcg) in 1 milligram (mg). To convert mg to mcg, multiply by 1,000. To convert mcg to mg, divide by 1,000. For example: 0.5 mg = 500 mcg, and 250 mcg = 0.25 mg.

Confusing mg with mcg creates a 1,000-fold dosing error, which can be fatal. For example, giving 1 mg of digoxin instead of 0.125 mg (125 mcg) is an 8x overdose. The ISMP lists mcg/mg confusion as a top cause of medication errors. Always verify units match the prescription.

Mcg (micrograms): levothyroxine, fentanyl patches, digoxin, vitamin D, folic acid, vitamin B12. Mg (milligrams): most common drugs like acetaminophen, ibuprofen, amoxicillin, metformin, lisinopril. G (grams): some IV antibiotics (e.g., ceftriaxone 1-2 g), electrolyte supplements.

IU (International Units) is a separate measurement system based on biological activity, not weight. It varies by substance: 1 IU of Vitamin D = 0.025 mcg. 1 IU of Vitamin A = 0.3 mcg retinol. IU cannot be directly converted to mcg/mg without knowing the specific substance.

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