How do I convert mcg to mg?
Divide the number of micrograms by 1,000 to get milligrams. 500 mcg ÷ 1,000 = 0.5 mg, because one milligram is 1,000 micrograms.
In practice that moves the decimal point three places to the left: 250 mcg becomes 0.25 mg and 50 mcg becomes 0.05 mg. To go from mg to mcg, multiply by 1,000 and the point moves three places to the right, so 0.3 mg is 300 mcg.
What is 100, 250 or 500 mcg in mg?
100 mcg is 0.1 mg, 250 mcg is 0.25 mg and 500 mcg is 0.5 mg. Every row in the table below is the same division by 1,000.
Micrograms to milligrams: divide by 1,000.
| Micrograms (mcg) | Milligrams (mg) |
|---|---|
| 50 mcg | 0.05 mg |
| 100 mcg | 0.1 mg |
| 125 mcg | 0.125 mg |
| 200 mcg | 0.2 mg |
| 250 mcg | 0.25 mg |
| 300 mcg | 0.3 mg |
| 400 mcg | 0.4 mg |
| 500 mcg | 0.5 mg |
| 750 mcg | 0.75 mg |
| 1,000 mcg | 1 mg |
| 2,500 mcg | 2.5 mg |
| 5,000 mcg | 5 mg |
Is 1000 mcg the same as 1 mg?
Yes. 1,000 mcg and 1 mg are the same amount written in two units, so a label that says one and a note that says the other describe the same quantity.
Is 400 mcg the same as 4 mg?
No. 400 mcg is 0.4 mg, and 4 mg is ten times that amount.
The same check applies to any pair of look-alike numbers. 5 mcg and 5 mg are not the same either: 5 mg is 5,000 mcg, a thousand times more. The converter above shows this line under every answer, because a number that reads correctly in the wrong unit is the error this page exists to catch.
Which is bigger, mg or mcg?
A milligram is bigger: one mg is 1,000 mcg. The unit describes how much of something there is, and says nothing about its strength or effect.
Why is a mix-up between mcg and mg so easy to make?
The two abbreviations differ by one letter, and a number usually looks plausible in either unit. A dose written in one and read in the other is out by a factor of 1,000, which is not a small error.
The ISMP list of error-prone abbreviations flags the µg symbol for this reason: it can be mistaken for mg, and ISMP recommends writing mcg instead. The same list recommends a zero before the decimal point (0.5 mg, not .5 mg) and none after a whole number (1 mg, not 1.0 mg), because a decimal point that is not seen turns either one into a tenfold error.
In peptide arithmetic the slip usually enters at one step. A vial is commonly labelled in mg while a dose is commonly written in mcg, so the conversion sits in the middle of the calculation. A useful sense check is the dose count: if the arithmetic says a vial holds a thousand times more doses than expected, the units have slipped somewhere. The field guide to mg, mcg, mL and units walks through the whole chain.