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Glossary

What does mcg mean on a supplement label?

Written by the Full Measure editorial team, which sells supplements. Approved for publication by the Full Measure owners. Updated .

Drafted with AI assistance from the sources listed below. How we write these

Quick answer

Mcg is the label abbreviation for microgram, one millionth of a gram. A milligram (mg) is one thousandth of a gram, so 1 mg equals 1,000 mcg. Labels use mcg for nutrients needed in tiny amounts, such as vitamin B12, whose Daily Value is 2.4 mcg.1,2

Key facts

  • The SI symbol for microgram is µg; US labels write mcg, the abbreviation set in FDA labeling rules.1,3
  • Nutrients with Daily Values in mcg include vitamins A, D, K and B12, folate, biotin, iodine, selenium, chromium and molybdenum.2
  • Labels must use the unit the FDA sets for each nutrient's Daily Value, which is why vitamin C appears in mg and vitamin D in mcg.4,5
  • Some mcg figures carry a suffix, mcg RAE for vitamin A and mcg DFE for folate, that adjusts for different forms of the vitamin.2,6

Grams, milligrams and micrograms

Metric weights on supplement labels1,6
UnitLabel abbreviationShare of a gramEquals
gramgone1,000 mg
milligrammgone thousandth1,000 mcg
microgrammcgone millionth0.001 mg

A thousandfold gap is easy to misread. A tablet with 1,000 mcg of vitamin B12 holds 1 mg, and 500 mcg of folic acid is half a milligram.1

Which nutrients are listed in mcg

Daily Values stated in micrograms2
NutrientDaily Value
Vitamin A900 mcg RAE
Vitamin D20 mcg
Vitamin K120 mcg
Vitamin B122.4 mcg
Folate400 mcg DFE
Biotin30 mcg
Iodine150 mcg
Selenium55 mcg
Chromium35 mcg
Molybdenum45 mcg

The other vitamins and minerals on the list, such as vitamin C, calcium, magnesium and zinc, have Daily Values in milligrams.2

Reading small numbers

Labels may show decimals for small amounts, such as 2.4 mcg, because the FDA lets makers add decimal places when whole numbers are too coarse to express a low amount.5

Vitamin D is the one nutrient where you may see two units on one line. The amount must be in mcg, and the maker may add the same amount in IU in parentheses, as in 25 mcg (1,000 IU).3,5

Questions people ask

Is mcg the same as mg?

No. A milligram is 1,000 times larger than a microgram. Mixing them up changes an amount a thousandfold, so check the unit as carefully as the number.1

Is mcg the same as µg?

Yes. Both mean microgram. µg uses the SI symbol for micro, and mcg is the form FDA labeling rules use.1,3

Why is vitamin D in mcg and not IU?

Since the 2016 label rule, vitamin D must be given in mcg; IU may follow in parentheses. 1 mcg equals 40 IU.3,5

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Sources

  1. National Institute of Standards and Technology. Metric (SI) Prefixes. Opened 2026-10-07.
  2. U.S. Food and Drug Administration. Daily Value on the Nutrition and Supplement Facts Labels. Content current as of March 5, 2024. Opened 2026-10-07.
  3. U.S. Food and Drug Administration. Converting Units of Measure for Folate, Niacin, and Vitamins A, D, and E on the Nutrition and Supplement Facts Labels: Guidance for Industry. August 2019. Opened 2026-10-07.
  4. U.S. Food and Drug Administration. Dietary Supplement Labeling Guide: Chapter IV. Nutrition Labeling. April 2005. Opened 2026-10-07.
  5. Code of Federal Regulations, Title 21, Section 101.36: Nutrition labeling of dietary supplements. Legal Information Institute, Cornell Law School (eCFR text). Opened 2026-10-07.
  6. Code of Federal Regulations, Title 21, Section 101.9: Nutrition labeling of food. Legal Information Institute, Cornell Law School (eCFR text). Opened 2026-10-07.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.