Free Tool
Unit Converter (mcg / mg / IU)
Convert a value between micrograms, milligrams, and international units. mcg↔mg is pure mass; any IU conversion uses a substance-specific IU-per-mg factor. General reference only — not medical advice.
Enter a value and units, then Convert.
How These Units Relate
1 mg = 1000 mcg
Pure mass — the same for every substance.
1 mg ≈ 3 IU
Somatropin / HGH reference (so 1 IU ≈ 0.333 mg).
IU ↔ mass varies
An IU measures activity, not mass — use each substance's own factor.
Micrograms and milligrams are both units of mass, so converting between them is a fixed factor of 1,000 (1 mg = 1,000 mcg). An international unit (IU), by contrast, measures biological activity, not weight — so the same number of IU can map to different milligram amounts depending on the substance. That is why every IU conversion above routes through milligrams using an IU-per-mg factor you supply. The default of 3 IU/mg is a common reference for somatropin (HGH); other preparations use different factors, so always check your product's labeling.
Educational reference only — not a recommendation to use, inject, start, stop, or change any substance or medication. Confirm the correct IU-per-mg factor against your product's labeling and your prescriber's guidance.
Related tools: Dosing Calculator · Reconstitution Calculator · All tools
Frequently Asked Questions
How do I convert mcg to mg?
Divide micrograms by 1,000. There are 1,000 mcg in 1 mg, so 500 mcg equals 0.5 mg and 250 mcg equals 0.25 mg. This is a fixed mass conversion that is the same for every substance.
How do I convert mg to IU?
Multiply milligrams by the substance's IU-per-mg factor. Unlike mcg↔mg, the IU↔mass relationship is not universal — it depends entirely on the specific substance and its potency. For somatropin (HGH), roughly 1 mg ≈ 3 IU, so 1 mg ≈ 3 IU and 2 mg ≈ 6 IU. Always use the factor listed on your product's labeling.
How many IU are in 1 mg of HGH?
For somatropin (HGH) a commonly cited reference is about 3 IU per mg, so 1 mg ≈ 3 IU and 1 IU ≈ 0.333 mg. This is a general estimate — confirm the exact factor on your specific product's labeling, as different preparations can vary.
Why does IU conversion need a separate factor?
An international unit (IU) measures biological activity, not mass, so the same number of IU can correspond to different milligram amounts depending on the substance. mcg and mg are pure mass units that convert directly, but converting to or from IU requires a substance-specific IU-per-mg factor.
Is 1000 mcg the same as 1 mg?
Yes. 1,000 micrograms (mcg) equals exactly 1 milligram (mg). This conversion never changes and applies to any substance because both are units of mass.
Should I rely on this converter for dosing?
Treat the result as a general educational estimate, not medical advice. Verify the IU-per-mg factor against your product's labeling and confirm any dose with your prescriber or clinician before acting on it.
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