What does mcg stand for? It is the abbreviation for microgram, a tiny unit of weight equal to one millionth of a gram. You will see it on vitamin bottles, nutrition labels and prescriptions, usually for nutrients and medicines that work in very small amounts, such as vitamin B12, vitamin D, folate and iodine.
The size is hard to picture. A single grain of table salt weighs far more than a microgram. That is why reading the unit correctly matters: mcg and mg look similar, but one is a thousand times larger than the other.
Quick facts
Stands for
MicrogramSize
One millionth of a gram, 1/1,000 of a milligramSymbol
µg (the Greek letter mu plus g)Type
Unit abbreviationPeriod or no period
No periodPlural
mcg, same as singularSeen on
Vitamin labels, prescriptions, nutrition factsNot to be confused with
mg, milligram
Microgram abbreviation: mcg and µg
The word microgram joins two parts. Micro is a metric prefix that means one millionth, and gram is the base unit of mass. The letters m, c and g come from the start of "micro" and from "gram."
Scientists use a different short form, µg, where µ is the Greek letter mu, the official metric symbol for micro. On labels and in medicine, though, mcg is common in the United States. A handwritten µ can look like an m, so a careless reader might see µg as mg and take a thousand times the right dose. Hospital safety groups recommend writing mcg for that reason.
What does mcg stand for compared with mg and g?
| Unit | Abbreviation | Equal to |
|---|---|---|
| Gram | g | 1,000 milligrams |
| Milligram | mg | 1,000 micrograms |
| Microgram | mcg or µg | 1/1,000 of a milligram |
So 1,000 mcg is the same as 1 mg, and 1,000,000 mcg makes a gram. A label that says 500 mcg could also be written as 0.5 mg. Read more about the larger units on the mg and gram abbreviation pages.
Reading mcg on a vitamin label
The Supplement Facts panel lists an amount for each nutrient and often a percent of the Daily Value. Nutrients needed in tiny amounts show mcg, while larger ones use mg.
On a multivitamin bottle: "Vitamin D 20 mcg (800 IU), Vitamin C 90 mg." The vitamin D amount is in micrograms, and the label also gives it in International Units, an older measure. For vitamin D, 1 mcg equals 40 IU. The vitamin C amount is in milligrams, a much bigger unit.
Folate is often listed as "mcg DFE," which stands for dietary folate equivalents. The extra letters adjust for the fact that the body absorbs folic acid from supplements more easily than folate from food.
How to write the mcg abbreviation
- Lowercase: write mcg, not MCG or Mcg, when you mean the unit.
- No period: metric unit abbreviations do not take one.
- No s for plural: 1 mcg and 250 mcg both use the same form.
- Space it out: type 50 mcg, with a gap after the number.
- Use a leading zero: if you ever need a decimal, write 0.5 mg, not .5 mg, so the dot is not missed.
Most people read mcg aloud as the full word, "microgram." Saying the letters "M C G" is also understood, especially at a pharmacy counter.
Where else MCG shows up
In capitals, the letters have a few unrelated meanings. Sports fans may know MCG as a large cricket stadium in Australia. In medicine, MCG can also mean magnetocardiography, a test that measures magnetic fields from the heart. On a supplement or prescription, though, mcg stands for the unit every time. For other short forms you see on labels and forms, visit the common abbreviations section.
Questions people ask
Is mcg the same as mg?
No. A milligram (mg) is 1,000 times larger than a microgram (mcg). Mixing them up can lead to a very wrong dose, so read the unit carefully.
How many mcg are in 1 mg?
There are 1,000 micrograms in 1 milligram. To change mcg to mg, divide by 1,000.
What is the abbreviation for microgram?
The usual abbreviation is mcg. The scientific symbol is µg, but mcg is preferred in medicine because it is harder to misread.
How do you convert mcg of vitamin D to IU?
Multiply by 40. For example, 25 mcg of vitamin D equals 1,000 IU.
Is mcg a lot?
No, it is a very small amount. Many vitamins and minerals are needed only in micrograms each day, which is why labels use this unit.