Micrograms to Milligrams Converter (mcg ↔ mg ↔ g)
Convert between micrograms (mcg / µg), milligrams (mg) and grams (g) in any direction, with a table of common medication and supplement strengths.
Last updated: October 2026
Converted amount
0.5 mg
This calculator gives an estimate for general information only. It is not medical advice and does not replace a doctor, pharmacist or other qualified health professional. Always check with them before acting on the result, especially for medication doses, children, pregnancy or a medical condition, and follow the guidelines of your local health authority.
Formula below · 3 sources (NIST, fda.gov, ismp.org) · Updated Oct 2026
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About this calculator
The prefix milli- means one thousandth and micro- means one millionth, so:
1 g = 1,000 mg = 1,000,000 mcg, and 1 mg = 1,000 mcg.
To convert mcg to mg divide by 1,000 (move the decimal point three places left). To convert mg to mcg multiply by 1,000. Grams are another factor of 1,000 in each direction. The calculator takes any of the three units in and gives the other two in the tiles.
mcg, µg and ug all mean microgram. The SI symbol is µg, but the FDA and the Institute for Safe Medication Practices recommend writing "mcg" in prescriptions and labels, because a handwritten or badly printed "µ" is read as "m" and turns 100 µg into 100 mg, a thousand-fold overdose. For the same reason a leading zero is written before a decimal (0.1 mg, never .1 mg) and a trailing zero never is (1 mg, never 1.0 mg).
When the unit matters most: drugs with narrow therapeutic ranges that are dosed in micrograms, such as levothyroxine (25-300 mcg), digoxin (62.5-250 mcg), fentanyl (patches in mcg per hour) and clonidine, and supplements such as vitamin B12, folate, vitamin D (25 mcg = 1,000 IU) and vitamin K that are labelled in mcg while other vitamins are labelled in mg. Always compare the number on the product with the prescription after converting both to the same unit.
Common microgram amounts in milligrams and grams
Scroll sideways to see all columns →
| Micrograms (mcg) | Milligrams (mg) | Grams (g) | Seen on labels as |
|---|---|---|---|
| 25 | 0.025 | 0.000025 | Levothyroxine 25 mcg, vitamin D 25 mcg (1,000 IU) |
| 50 | 0.05 | 0.00005 | Levothyroxine 50 mcg, fentanyl patch 50 mcg/h |
| 100 | 0.1 | 0.0001 | Levothyroxine 100 mcg, vitamin D 100 mcg (4,000 IU) |
| 250 | 0.25 | 0.00025 | Digoxin 0.25 mg (250 mcg) |
| 500 | 0.5 | 0.0005 | Digoxin 0.5 mg, cyanocobalamin 500 mcg |
| 1,000 | 1 | 0.001 | Vitamin B12 1,000 mcg = 1 mg, folic acid 1 mg |
| 5,000 | 5 | 0.005 | Biotin 5,000 mcg = 5 mg |
How to use
Pick the direction and enter the amount; the tiles show the value in all three units. Example (the defaults): 500 mcg → mg. 500 ÷ 1,000 = 0.5 mg (a digoxin 0.5 mg loading dose is 500 mcg). Example mg → mcg: a prescription reads 0.075 mg of levothyroxine and the bottle says 75 mcg. 0.075 × 1,000 = 75 mcg, so they match. Example mg → g: a 1,500 mg dose of an antibiotic is 1,500 ÷ 1,000 = 1.5 g, and 500,000 mcg is 0.5 g.
Frequently asked questions
How many mcg are in a mg?
1,000. A milligram is a thousandth of a gram and a microgram a millionth, so there are 1,000 micrograms in every milligram and 1,000,000 in a gram. 0.5 mg is 500 mcg; 0.025 mg is 25 mcg.
What is the difference between mcg and µg?
None; both are the microgram. µg is the SI symbol, mcg the safer spelling that the FDA and ISMP recommend on prescriptions because µ is easily misread as m. "ug" is the same unit typed without the Greek letter.
Why does my prescription say 0.1 mg but the tablet says 100 mcg?
They are the same dose: 0.1 × 1,000 = 100 mcg. Prescribers and manufacturers sometimes use different units for the same strength. After converting, the numbers should agree exactly; if they do not, ask the pharmacist before taking the medicine.
How do I convert IU to mcg?
International units are drug-specific, so there is no single factor. For vitamin D, 1 mcg = 40 IU (25 mcg = 1,000 IU); for vitamin A, 1 mcg of retinol = 3.33 IU; for vitamin E, 1 mg of natural alpha-tocopherol = 1.49 IU. Check the product label or monograph for the substance you have.
Can I convert mcg or mg to mL?
Only with the concentration of the liquid (for example 50 mcg/mL or 160 mg per 5 mL). Convert the dose to the unit the concentration uses, then divide by the concentration; our mg to mL calculator does this step.
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Sources & references
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