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Peptide Guide · Free tools

Peptide dose converter

mcg to mg and back for any peptide, and IU for somatropin, where a fixed standard exists.

Weight: 1 mg = 1,000 mcg
Somatropin: 1 mg = 3 IU (WHO standard)
HCG: No fixed factor: use the IU on the label

Micrograms

mcg

Milligrams

International units

IU is off for this setting: most peptides are dosed by weight and have no IU value. Pick somatropin to convert IU.

The short answer

One milligram (mg) is 1,000 micrograms (mcg), so divide mcg by 1,000 to get mg. IU measures biological activity, not weight, so it converts to mg only where a fixed standard exists. For somatropin (human growth hormone), 1 mg equals 3 IU. HCG has no fixed factor; use the IU on the label.

Medically reviewed by Robert Lufkin, MD (opens in a new tab)

Chief Medical Officer, Vitals Vault · Updated October 29, 2026 · 4 sources

How mcg, mg and IU relate

Weight: mcg and mg

1 mg = 1,000 mcg, and 1 g = 1,000 mg. 250 mcg is 0.25 mg; 3.21 mg is 3,210 mcg. These hold for every substance.¹

Activity: IU

An international unit measures biological effect against a reference standard, so its weight differs from one substance to the next. Never borrow one product’s IU factor for another.

Where IU converts

Somatropin has a fixed standard: 1 mg = 3 IU, so 3.21 mg is 9.63 IU. HCG is labeled in IU from a bioassay with no single mg factor, so use the IU on the label.²³⁴

From conversion to syringe units

Converting is step one. To turn a dose into a reading on an insulin syringe you also need the vial strength and how much liquid it was mixed with. The peptide dosage calculator does both and shows the draw on a U-100 scale.

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Measure before you start

The math tells you what to draw. Only a blood test before you start, and a retest after, shows what a peptide changed for you.

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Dose converter questions

How many mcg are in 1 mg?

There are 1,000 micrograms (mcg) in 1 milligram (mg). To go from mcg to mg, divide by 1,000; from mg to mcg, multiply by 1,000.

Is mcg the same as µg?

Yes. µg and mcg both mean microgram. Pharmacies often write mcg so it is not misread as mg.

Can IU be converted to mg for every peptide?

No. IU measures biological activity against a reference standard. Only a substance with a fixed standard, such as somatropin at 3 IU per mg, converts reliably. Most peptides are dosed in mg or mcg and have no IU value.

How many IU are in 1 mg of HGH?

For somatropin (human growth hormone), 1 mg is 3 IU, the factor set by the WHO International Standard. So 4 IU is about 1.33 mg.

Why does the converter not give an mg value for HCG?

HCG is labeled in IU from a bioassay, and activity per mg differs between products and sources. A single mg factor would be wrong for some vials, so use the IU printed on your label.

How does this fit with the dosage calculator?

Convert first, then calculate. The dosage calculator takes the vial in mg and the dose in mcg or mg, and returns the units to draw on a U-100 syringe.

Is this a dosing recommendation?

No. It converts units only. Your dose comes from a licensed clinician, and the converter cannot check a product’s identity, purity or strength.

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Sources

Built by the Vitals Vault editorial team, medically reviewed by Robert Lufkin, MD, and updated October 29, 2026. General education, not medical advice. This calculator converts a dose your clinician has already set into a syringe reading. It does not choose a dose, check whether a product is right for you, or replace your pharmacy’s instructions. Always follow the label and the clinician who prescribed it.