International units

An international unit measures activity against a reference standard, not a mass. The conversion belongs to one preparation, so the potency is a field rather than a table.

Educational arithmetic only. Not medical advice and not a dosing protocol.

Fill the fields in and the answer appears here.

This tool does its arithmetic in the browser, so it needs JavaScript switched on. The arithmetic is one division by the potency: see the steps below.

What the bench will not tell you

This is educational arithmetic on figures entered by the reader. It is not medical advice, not a dosing protocol, and not a recommendation that anything be prepared, obtained or administered.

Nothing here states what quantity is appropriate for anyone, and there is no function in it that produces an amount to administer. A question about anyone’s health belongs with a licensed clinician who can examine the person asking.

Compounds of the kind this arithmetic is used on are largely research chemicals that are not approved by the FDA for human use. An exact calculation is not an accurate measurement: what is actually in a syringe depends on the preparation and the device, neither of which this page can see.

No qualified clinical reviewer is recorded against this site, and no credential is claimed anywhere on it. the limits of this bench.

The arithmetic, step by step

mass in mg = IU / (IU per mg). Thirty IU of a preparation labelled 3,000 IU per mg is 30 / 3000 = 0.01 mg, which is 10 micrograms.
The other direction is the multiplication: IU = mass in mg × IU per mg.
The potency has to come from the preparation. An international unit is defined against a biological reference standard, one substance at a time, and has no mass equivalent that holds across substances or even across formulations of one substance.

Why there is no IU table on this page

Because a built-in table would be a claim about a vial this bench has never seen. The IU-per-milligram figure is a property of a specific preparation, established by assay against a reference standard. Two vials of nominally the same thing can carry different figures, and a converter that hides that behind a lookup is confidently wrong whenever it matters.

Asking for the number has a second benefit: it makes the reader look at the label. The potency is printed there, and a figure read off the container in hand beats a figure averaged across a category every time.

What an international unit is actually measuring

Biological activity, expressed in a unit defined by an international reference preparation rather than by any physical quantity. That is why it exists: for substances where mass is a poor proxy for effect, a unit defined by assay is more useful than a unit defined by weight.

It also means the conversion runs only one way with confidence. Given a potency, IU and mass convert exactly. Without one, no amount of arithmetic recovers it, and the honest output is a refusal rather than an estimate.

Next to this on the bench

Mass and volume units
Where no outside figure is needed.
Volume for an amount
Once the IU figure is a mass.
The limits of this bench
Stated at full length.