Peptide unit converters.
Mass-to-activity converters for peptides labelled in International Units. These pages handle the IU-to-mg ratios that come from biological-activity standards — a different arithmetic from the vial-to-syringe math handled by the reconstitution calculator.
- Somatropin mg to IU
Convert milligrams of somatropin (recombinant HGH) to International Units at the standard 3 IU per mg ratio. Lookup table from 0.1 mg to 30 mg.
- Somatropin IU to mg
Reverse direction — convert IU values back to mg. Lookup table from 1 IU to 100 IU plus common compounded mg vial sizes.
Why mg and IU disagree, and which one your vial uses
Most research peptides are quantified in milligrams — a direct mass measurement that comes off a balance and lines up with how the powder is weighed during compounding. A handful of compounds are quantified in International Units instead. International Units are a biological-activity unit: an IU is defined against a reference preparation with a stated effect at the receptor, so the value tracks expected pharmacological response rather than raw molecular weight. Somatropin and HCG are the most common IU-labelled peptides on this site; insulin is the third historical example and is referenced in some related calculations.
For somatropin specifically, the WHO reference standard fixes the conversion at approximately 3 IU per milligram, so a 10 IU vial corresponds to roughly 3.33 mg of recombinant human growth hormone. Different brands — Genotropin, Humatrope, Norditropin, Saizen, Omnitrope — print the IU value on the carton because that is how clinical doses are written, even when an underlying mg specification exists. Compounded research-grade vials sometimes invert the convention and print mg, which is why a converter is useful: the protocol you are following may state one unit while the vial in front of you uses the other.
The two converters below cover both directions. Each page renders a static lookup table so the value can be checked without typing into a calculator, plus a worked example for the most commonly bought vial sizes. The arithmetic is intentionally transparent — the math is the same 1 mg = 3 IU constant applied across a range, not a black-box transformation.
Frequently asked questions about unit conversions
- Why are some peptides labelled in IU instead of mg?
- International Units measure biological activity rather than mass. For compounds where the active conformation matters as much as the raw protein weight — somatropin, HCG, insulin — historical reference standards fixed an IU value that maps to an expected receptor-level effect. Mass-based labelling was added later, which is why a single vial can carry both "10 IU" and "3.33 mg" on its packaging. The IU-to-mg ratio is compound-specific; somatropin is the canonical 1 mg ≈ 3 IU case, while HCG uses a different activity standard.
- Are these converters the same as the reconstitution calculator?
- No — they answer different questions. The unit converters on this page handle the static activity-to-mass ratio printed on a vial. The reconstitution calculator under /calculator handles the dynamic vial-size × BAC-water × dose math that decides how many U-100 insulin-syringe units a given dose requires. You typically use a unit converter once (to interpret a label) and the reconstitution calculator every time you draw a syringe.
- Is the 1 mg = 3 IU somatropin ratio exact?
- It is a clinical convention rooted in the WHO somatropin reference standard, not a precise physical-chemistry constant. Recombinant batches typically test between 2.9 and 3.1 IU per mg of pure protein. Pharmacy labelling rounds to exactly 3 for practical dosing, so a 10 IU vial is treated as 3.33 mg even though the actual mass may differ by a percent or two. The converters on this page use the labelling convention.
PeptideDose is an educational reference. It is not medical advice and does not replace consultation with a licensed healthcare provider. Doses shown in presets are derived from published protocols and product labels — they are not personal recommendations.