mg is short for milligram. mcg is short for microgram. Both describe mass—how much of a substance is present—not liquid volume.
1 mg = 1,000 mcg
When the number is expressed in micrograms, it is 1,000 times larger, but the physical amount has not changed.
How to convert mg to mcg
Multiply the number of milligrams by 1,000.
Example: 0.25 mg × 1,000 = 250 mcg.
How to convert mcg to mg
Divide the number of micrograms by 1,000.
Example: 750 mcg ÷ 1,000 = 0.75 mg.
Quick conversion table
| Milligrams (mg) | Micrograms (mcg) |
|---|---|
| 0.01 mg | 10 mcg |
| 0.1 mg | 100 mcg |
| 0.25 mg | 250 mcg |
| 0.5 mg | 500 mcg |
| 1 mg | 1,000 mcg |
| 5 mg | 5,000 mcg |
What mg and mcg are not
They are not milliliters (mL), which measure liquid volume, and they are not the numbered units printed on a syringe. To relate mass and liquid volume, you need a concentration expressed as mass per volume, such as mg/mL.
Important: Confusing mg with mcg changes a number by a factor of 1,000. Checking the arithmetic does not determine whether a substance, amount, or measurement method is safe.
Frequently asked questions
Is 1 mg the same as 1,000 mcg?
Yes. They describe exactly the same mass.
Is 100 mcg the same as 1 mg?
No. 100 mcg equals 0.1 mg.
Does 1 mg always equal the same number of mL?
No. You need the concentration (mg/mL) to convert between mass and liquid volume.