IU to Mg Converter (HCG & HGH)

The IU to mg converter on this page turns International Units into milligrams and micrograms — and back again — using a potency factor you set for your specific compound. The critical thing to understand before you use it is that there is no single, universal IU-to-mg conversion. An International Unit measures biological activity, not mass, so the number of IU in one milligram is different for every substance. Enter the right factor and the math is exact; guess it and the answer is meaningless.

Below the converter you will find why the factor is compound-specific, the exact formulas the tool runs, a fully worked HGH example built on the standard 3 IU per mg figure for somatropin, a separate HCG example based on a reconstituted 5000 IU vial, and quick-reference tables. Everything here is written as a research reference for laboratory context only — it is dosing arithmetic, not medical advice.

Why there is no universal IU-to-mg conversion

An International Unit (IU) is defined by the effect a substance produces, measured against a World Health Organization International Standard — a physical reference preparation held for that one substance. Because each standard is calibrated independently, one IU of somatropin, one IU of HCG, one IU of insulin and one IU of a vitamin all correspond to completely different masses. There is no conversion that works across compounds, which is exactly why a converter has to ask you for a potency factor instead of assuming one.

Some peptides, such as HCG and other gonadotropins, are standardised and labelled almost entirely in IU because their activity is what matters and their mass is tiny and variable. Others, such as most research peptides, are sold and dosed in milligrams or micrograms. Somatropin (recombinant human growth hormone) sits in the middle: it is frequently labelled in IU on the vial yet discussed in mg, so it is the compound people most often need to convert.

How the IU to mg converter works

The tool applies a single potency factor in both directions. Set the factor once, then enter any amount in IU, mg or mcg and the other two update instantly.

Step 1 — Set the potency factor (IU per mg)

This is the only number that carries any compound-specific meaning, so it matters most. For somatropin, the widely used factor is approximately 3 IU per mg. Use the HGH / Somatropin preset for that value, or type your own factor for any other compound. If your product does not state a specific activity in IU per mg, you cannot reliably convert it, and you should dose it in the unit printed on the label instead of converting.

Step 2 — Enter an amount and its unit

Type the quantity you have and tell the tool whether it is in IU, mg or mcg. Internally the converter first reduces everything to milligrams, then expresses that same quantity in all three units. Because every output is derived from the identical underlying value, the three tiles always agree.

Worked example: HGH / somatropin at 3 IU per mg

Somatropin’s standard factor of about 3 IU per mg is the single most common conversion people search for. Suppose a vial is labelled 10 IU and you want to know the mass.

1. Factor: 3 IU per mg for somatropin.
2. Convert 10 IU to mg: 10 ÷ 3 = 3.33 mg.
3. Express in mcg: 3.33 mg × 1000 = 3,333 mcg.
4. Check it backwards: 3.33 mg × 3 = 10 IU. It reconciles.

The table below applies the 3 IU per mg factor across the amounts people most often need. Remember it is valid for somatropin only — do not reuse these numbers for a different compound.

Worked example: a 5000 IU HCG vial reconstituted

HCG is the classic case where you should not convert to mg at all. It is standardised and handled in International Units, and the milligram mass in a vial is minuscule and preparation-dependent. What you actually need is how many IU sit in each millilitre after you add water — the same reconstitution arithmetic used for any peptide, but kept entirely in IU.

Take a 5000 IU vial reconstituted with 2 mL of bacteriostatic water:

1. Concentration: 5000 IU ÷ 2 mL = 2,500 IU per mL.
2. Draw volume for a 500 IU amount: 500 ÷ 2,500 = 0.2 mL.
3. On a U-100 syringe: 0.2 mL × 100 = 20 units.
4. Amounts per vial: 5000 ÷ 500 = 10.

Converting mcg and mg to IU

Going the other way is just the same factor in reverse, with a units step. Micrograms convert to milligrams first (divide by 1000), then milligrams convert to IU (multiply by the factor). For somatropin at 3 IU per mg: 500 mcg is 0.5 mg, and 0.5 mg × 3 = 1.5 IU. The converter above chains both steps for you, and the live equation shows exactly which numbers it used.

If you are moving between mg and mcg only — with no IU involved — no factor is needed at all, because that relationship is universal: 1 mg always equals 1000 mcg. The compound-specific factor only enters the moment IU appear.

Common mistakes this converter prevents

• Assuming a universal factor. Applying somatropin’s 3 IU per mg to HCG, insulin or a vitamin produces a nonsense mass. Always reset the factor for each compound.
• Converting a compound that should stay in IU. HCG and similar gonadotropins are dosed in IU; converting them to mg adds error without adding usefulness.
• Mixing mcg and mg. Forgetting the 1000× step between micrograms and milligrams throws the IU result off by a factor of a thousand.
• Trusting a factor the label does not support. If the product sheet gives no IU-per-mg specific activity, there is no honest conversion — dose in the labelled unit.

Where to go next

Once you know the mass or activity you are working with, the practical next step is reconstitution. To turn a vial into syringe units, use the peptide dosage calculator, and for the full method — water volume, mixing and storage — read the peptide reconstitution guide. For compound-specific reference figures, see the HGH 10 IU vial protocol and the HCG 5000 IU vial protocol. If a term here is unfamiliar, the peptide glossary defines International Units, specific activity and reconstitution in plain language.