Dietary supplement labels: What are 'international units'?

content provided by

Dietary supplement labels: What are 'international units'?


The label on a bottle of vitamins lists "IU." What does that mean? Also, what's the difference between "mcg" and "mg"?



Scientific units, such as "IU," "mg" and "mcg," are different ways of measuring the amounts of vitamins and minerals in each tablet or capsule.

On the label of dietary supplements, "mg" refers to milligrams and "mcg" to micrograms. These are metric units for expressing weight. A milligram is 1/1000 of a gram, and a microgram is 1/1000 of a milligram. These are common units of measurement for minerals and some vitamins, such as vitamin C.

"IU" stands for International Units, which is an international standard of measurement for vitamins A, D and E. There's no fixed definition for IU, as there is for milligrams or micrograms. It's based on the potency of the substance, so the IU will be different for each substance. For example, one IU of vitamin A equals 0.3 micrograms, but one IU of vitamin E will equal one milligram.

Other information on dietary supplement labels includes:

  • Serving size. This is the manufacturer's suggested serving. It's normally stated as per tablet, per capsule, per packet or per teaspoonful.
  • Daily Value (DV). The Daily Value is the average amount of the vitamin or mineral that is needed to meet the nutritional requirements of a person of at least age 4 years. The number shown will be the percent of the daily value that one serving of the supplement provides.

If you have any questions about information found on supplement labels, talk to a pharmacist.

Last Updated: 05/27/2005
© 1998-2016 Mayo Foundation for Medical Education and Research (MFMER). All rights reserved. A single copy of these materials may be reprinted for noncommercial personal use only. "Mayo," "Mayo Clinic," "," "Mayo Clinic Health Information," "Reliable information for a healthier life" and the triple-shield Mayo logo are trademarks of Mayo Foundation for Medical Education and Research.

Terms and conditions of use


Bookmark and Share   E-Mail Page   Printer Friendly Version