Mg vs Mcg
Mg vs mcg comes down to one number: 1,000. A milligram (mg) is 1,000 times bigger than a microgram (mcg). So 1 mg holds 1,000 mcg, and 1 mcg is a tiny 0.001 mg.
Paste this code into your page. It shows the converter with one plain credit link.
The short answer
| Milligram | Microgram | |
|---|---|---|
| Written as | mg | mcg (also µg or ug) |
| Part of a gram | one thousandth | one millionth |
| In grams | 0.001 g | 0.000001 g |
| In the other unit | 1 mg = 1,000 mcg | 1 mcg = 0.001 mg |
| Which is bigger | bigger | smaller |
Both are units of mass in the metric system. The prefixes come from the SI system that NIST, the US measurement lab, lists. "Milli" means one thousandth and "micro" means one millionth.
How big is the gap?
Picture a gram split into 1,000 equal bits. Each bit is a milligram. Now split one of those bits into 1,000 more. Each of those is a microgram.
So the step from mg to mcg is the same size as the step from g to mg. Both steps are 1,000. To see the gram step, read mg to g.
| Grams (g) | Milligrams (mg) | Micrograms (mcg) |
|---|---|---|
| 1 | 1,000 | 1,000,000 |
| 0.1 | 100 | 100,000 |
| 0.001 | 1 | 1,000 |
| 0.000001 | 0.001 | 1 |
How to switch between mg and mcg
- From mg to mcg, multiply by 1,000. 0.2 mg × 1,000 = 200 mcg. The mg to mcg converter does it for you.
- From mcg to mg, divide by 1,000. 200 mcg ÷ 1,000 = 0.2 mg. Use the mcg to mg converter for this side.
A good self check: the mcg number is always the bigger number, because the unit is smaller.
Why people mix them up
The two units look alike and sound alike. A label may also use µg, the official symbol for a microgram. The Institute for Safe Medication Practices (ISMP) lists µg as a symbol that gets read as mg. That is why it asks people to write mcg. The what is mcg page covers all three ways of writing it.
The same number with a different unit is a very different amount. 100 mcg is 0.1 mg. 100 mg is 100,000 mcg. That gap is 1,000 times.
Two more writing habits from the same ISMP list help:
- Use a leading zero: 0.1 mg, not .1 mg.
- Drop the trailing zero: 1 mg, not 1.0 mg.
Where you see each unit
Labels tend to switch to mcg when an amount gets very small, so the number does not need a long string of zeros. On US supplement and food labels, the FDA requires vitamin D in mcg. It also uses mcg for vitamin A (as mcg RAE) and folate (as mcg DFE). The supplement label guide explains those extra letters.
Mg and mL are a different pair. One is mass and one is volume, so you cannot swap them without more facts.
Questions
Which is bigger, mg or mcg?
A milligram is bigger. One mg is the same as 1,000 mcg, so a microgram is only one thousandth of a milligram.
What is the difference between mg and mcg?
Size. Both measure mass, but 1 mg is 1,000 times more than 1 mcg. Multiply mg by 1,000 to get mcg, and divide mcg by 1,000 to get mg.
Is mcg the same as mg?
No. They are two units, and 1 mg equals 1,000 mcg. The same number in each unit is a very different amount.
How many micrograms are in a milligram?
There are 1,000 micrograms in one milligram. So 3 mg is 3,000 mcg.
Sources
- The International System of Units (SI), NIST Special Publication 330, 2019 edition, Table 7 SI prefixes and Table 8 non-SI units such as the liter, National Institute of Standards and Technology (NIST), doi:10.6028/NIST.SP.330-2019, read 2026-10-04
- Metric (SI) Prefixes, National Institute of Standards and Technology (NIST), read 2026-10-04
- ISMP List of Error-Prone Abbreviations, Symbols, and Dose Designations, Institute for Safe Medication Practices, 2021, read 2026-10-04
- Converting Units of Measure for Folate, Niacin, and Vitamins A, D, and E on the Nutrition and Supplement Facts Labels, US Food and Drug Administration, August 2019, read 2026-10-04