Unit Converter

The converter above handles the easy case: metric mass. Grams, milligrams, and micrograms differ by fixed factors of 1,000, so converting between them is pure multiplication. The traps are notational, not mathematical. Peptide vials are labeled in mg while research literature often reports amounts in mcg, so the same protocol can mix both units in one sentence, and the abbreviation "mcg" is used precisely because the scientific symbol µg is easily misread as mg in handwriting and low-resolution print.

International Units are a different kind of quantity entirely. An IU measures biological activity — how much effect a preparation produces in a standardized assay — not how much it weighs. The bridge between IU and mass exists only per substance, set by international reference standards. For somatropin (recombinant human growth hormone), the WHO's second international standard defines a specific activity of 3.0 IU per mg of somatropin (Bristow & Jespersen, Biologicals 2001), which is where the familiar "1 mg ≈ 3 IU" figure comes from. Insulin in the United States is formulated at 100 units per ml — the U-100 standard that insulin syringes are graduated to match (Donnor & Sarkar, Endotext). Substances like hCG have no meaningful mass equivalent at all and are quantified purely in IU.

Where conversions go wrong

Two errors account for most unit confusion. The first is the thousandfold slip between mg and mcg — easy to make, hard to notice, and large enough to matter. The second is treating IU as convertible without knowing the substance: an IU of one compound has no relationship to an IU of another, and applying somatropin's 3 IU/mg to anything else produces a meaningless number. This page converts quantities; it says nothing about what quantity of anything is appropriate — see the medical disclaimer.

How many mcg are in a mg? One milligram equals 1,000 micrograms, and one gram equals 1,000 milligrams. Every step on the metric mass ladder is a factor of 1,000, which is convenient but also the reason unit slips produce thousandfold errors — 0.25 mg and 250 mcg are the same amount written two ways, but 250 mg is a thousand times more.

Can I convert IU to mg? Only for a specific substance with a defined potency standard, because an International Unit measures biological activity rather than mass. For somatropin (recombinant human growth hormone), the WHO international standard assigns a specific activity of 3.0 IU per mg, so 1 mg ≈ 3 IU. That ratio applies to somatropin only — a generic IU-to-mg conversion does not exist.

Are syringe "units" the same as IU? No, and confusing them is a classic error. A unit marking on a U-100 syringe is a volume: 1/100 of a milliliter. An IU is a quantity of biological activity. They coincide for U-100 insulin only because that product is deliberately formulated at 100 IU per ml so the syringe scale reads activity directly. For any other solution in the same syringe, the markings are just hundredths of a milliliter.

Why are peptide doses usually written in mcg? Because research peptides are typically active at sub-milligram amounts, while vials are labeled in mg for practical weighing. A 5 mg vial expressed in the same unit as a 250 mcg figure would be 5,000 mcg — keeping doses in mcg and vials in mg avoids strings of zeros, at the cost of requiring a 1,000× conversion between the two.