What is a Microgram?

The microgram equals one millionth of a gram (10⁻⁶ g) and is the standard unit for very small mass measurements in pharmacology, environmental science, and trace-element nutrition. The Greek letter µ (mu) represents the SI prefix 'micro' (one millionth). Vitamin B12 daily intake is around 2.4 µg, and the lethal dose of botulinum toxin is in the nanogram-to-microgram range, making it one of the most potent biological substances known. The microgram is critical in air-quality monitoring (PM concentrations in µg/m³), trace-mineral supplements (selenium, iodine), and pharmaceutical compounding. It relates to the milligram (1,000 µg = 1 mg) and the nanogram (1,000 ng = 1 µg). Environmental regulators set legal limits on heavy metals (lead, arsenic) in drinking water in micrograms per liter.

Visual reference for how the microgram relates to other weight units. Each row links to the full converter for that pair.

• Vitamin D, A and K dosing
• Trace metal content in food and water
• Hormone replacement therapy dosing

• ✓1 µg = 0.001 mg = 1/1,000,000 g.
• ✓Some older labels write "mcg" instead of µg — both mean the same thing.
• ✓For very small doses prefer µg to avoid decimal confusion (0.025 mg vs. 25 µg).

• ✗Treating mcg and mg as equivalent on older prescription pads.
• ✗Typing "mg" when the intended unit is "µg" — a 1000× overdose.
• ✗Reading µg as g without the prefix — a 1-million-fold error.