Convert medication and supplement doses between micrograms (mcg/µg), milligrams (mg), grams and nanograms.
Health • mass dose
All 4 units on the mcg to mg Converter are defined against the Milligram (mg), so each result is one conversion factor away from a single reference rather than the end of a chain of roundings.
The conversion this page is most often opened for is ready before you type anything: 1 mcg = 0.001 mg. Change either side and every row in the table recalculates with it.
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Supplement and medication labels mix units: 1 milligram (mg) = 1,000 micrograms (mcg, also written µg). Converting between mcg, mg, grams and nanograms prevents dosing mistakes when comparing products or following a prescription.
Note that IU (international units) are substance-specific — for vitamin D, 1 mcg = 40 IU, while vitamin E differs — so check your label. This tool handles the metric mass units; always confirm dosing with a pharmacist or doctor.
The nanogram row at the small end belongs to analytical work rather than to dosing. Hormone assays, drug monitoring and environmental contaminant results are commonly reported in nanograms per millilitre or per litre, so a laboratory value and a supplement label can differ by a factor of a million while describing the same substance. Reading a result without registering which of the three prefixes it carries is a far more common error than any arithmetic mistake in converting between them.
International units are not a mass unit at all and cannot be converted here without naming the substance, because an IU is defined by biological activity rather than by weight. For vitamin D, 1 microgram is 40 IU. For vitamin A the relationship runs through retinol activity equivalents, with 1 IU of retinol equal to 0.3 micrograms. Vitamin E is different again, and the factor depends on whether the form is natural or synthetic — roughly 1.49 IU per milligram for the natural isomer against 2.22 for the synthetic mixture. One conversion factor applied across all three is wrong twice.
A final distinction worth keeping separate is concentration against dose. A vial labelled in milligrams per millilitre states how much substance is present per unit volume, not how much is being given; the dose depends on the volume drawn. Confusing the two is a recognised source of medication error, and it is why prescriptions specify a mass and a volume rather than trusting either alone. Anything converted on this page is a quantity of substance, and turning it into a dose still requires the strength of the preparation in hand.
Quick reference — 1 Microgram (mcg) is equal to:
| Nanogram | ng | 1,000 |
| Milligram | mg | 0.001 |
| Gram | g | 0.000001 |
4 units of mcg to mg, each a fixed multiple of the mg. The table spans 1,000,000,000:1, from ng (0.000001 mg) to g (1000 mg). Conversion is one multiplication into the base unit and one division out of it, with no lookup table and no approximation.
value_to = value_from × (factor_from ÷ factor_to)1 ng = 0.000001 mg1 mcg = 0.001 mg1 mg = 1 mg1 g = 1000 mgwhere:
Assumptions: Factors are exact definitions. Full double precision is carried internally and rounding is applied only for display.
Result25 mcg = 0.025 mg
A milligram is one thousand micrograms. The arithmetic is trivial; the consequences of getting it wrong are not, which is why this conversion has its own tool.
Medicine treats it as a safety issue rather than a units issue. The abbreviation "µg" is widely discouraged in handwritten prescribing because a poorly formed µ can be read as an m, turning a dose into a thousand times itself — so guidance is to write "microgram" in full. The same factor appears in nutrition labelling, where vitamin D moved from international units to micrograms and vitamin A is quoted in retinol activity equivalents, and in laboratory work, where µg/dL and mg/L describe the same measurement at different scales.