Peptide amounts are quoted in milligrams (mg), micrograms (mcg) and sometimes international units (IU). This converter moves between metric mass units instantly, and — when you supply a conversion factor — estimates IU.
Metric conversions are fixed
Mass units always relate by factors of 1,000, so mg ↔ mcg is a clean, universal conversion:
| Unit | Equals |
|---|---|
| 1 mg | 1,000 mcg |
| 1 mcg | 1,000 ng |
| 1 mg | 1,000,000 ng |
How do you convert mg to IU?
An international unit (IU, sometimes written UI) measures biological activity, not mass. Because of that there is no universal mg ↔ IU conversion — the ratio is different for every substance and depends on how potent that specific preparation is. The factor is set for each compound and is usually printed on the vial label or the certificate of analysis (CoA).
Once you know the factor for your compound, the maths is simple:
- mg → IU: IU = mg × (IU per mg)
- IU → mg: mg = IU ÷ (IU per mg)
Enter your factor (as mg per IU) in the tool above and it will estimate IU alongside the fixed mass conversion. Without a factor, any "mg to IU" or "IU to mg" answer is meaningless.
Worked examples
These use an illustrative factor only — always use the factor for your own product.
- How many mg is 10,000 IU? If a compound is labelled at 3 IU per mg (a common example figure for somatropin/HGH), then 10,000 IU ÷ 3 ≈ 3,333 mg. At a different factor you get a completely different answer.
- 25,000 IU to mg? At the same example 3 IU/mg factor, 25,000 IU ÷ 3 ≈ 8,333 mg.
- How many mg is 1 IU? With an example 3 IU/mg factor, 1 IU ≈ 0.33 mg. "How many mg in an IU" always depends on the compound.
- HGH calculator style: a vial marked "10 mg = 30 IU" is telling you its own factor of 3 IU/mg. Use that printed number, not a generic one.
Example IU/mg factors (illustrative only)
The values below are examples to show the idea — they are not authoritative and vary by product. Always read the figure on your vial or CoA.
| Compound | Example factor | Meaning |
|---|---|---|
| Somatropin / HGH | ~3 IU per mg | 1 mg ≈ 3 IU (so 1 IU ≈ 0.33 mg) |
| hCG | set per batch (often thousands of IU per mg) | Read the exact number from the label |
IU is not mcg
IU and mcg are not interchangeable. mcg is a fixed mass unit; IU is a measure of activity that only maps to a mass once you apply the compound's factor. Converting mcg ↔ IU still needs that same factor.