Milligram (mg) – most bulky vitamins and minerals are measured this way. 1000 milligrams make a gram.

Microgram (mcg) – 1000 th of a milligram (i.e. 1000 micrograms = 1 milligram). This measure is appropriate for trace minerals like Chromium and Selenium. B_12, K₂ and Folic acid are typically measured in micrograms. Don’t be fooled by labels that list use micrograms where milligrams would be more appropriate. For example, mass market multivitamins sometimes include Lycopene or Lutein in microgram quantities. That borders on fraudulent since they are only putting in a tiny fraction of what was shown in studies to be useful.

IU – International units – This measure is used for oil-soluble vitamins A, D and E.