About

In pharmacology and nutrition, mass is not always the best measure of potency. The International Unit (IU) is a unit of measurement for the amount of a substance, based on its biological activity or effect rather than its weight. This creates a significant challenge: there is no single conversion factor. 1 mg of Vitamin E has a completely different IU value than 1 mg of Vitamin A.

This tool solves the complexity of substance-specific conversions. It utilizes a validated database of conversion factors defined by health organizations. Whether you are formulating a supplement, checking a prescription, or comparing nutritional labels, this calculator applies the correct biological coefficient for the specific substance you select, ensuring safety and accuracy in dosage.

Formulas

The formula depends entirely on the biological equivalence factor ($k$) of the substance. The general logic converts the input mass to the base unit of the factor (usually micrograms or milligrams) and then divides by the factor.

IU = Mass_inputk_substance

For example, for Vitamin D, the standard is 1 IU = 0.025 μg. To convert 1 mg (1000 μg):

IU = 1000 μg0.025 μg/IU = 40,000 IU

Reference Data

Substance	1 IU Equivalent	1 mg converts to
Vitamin A (Retinol)	0.3 mcg	3,333 IU
Vitamin A (Beta-carotene)	0.6 mcg	1,667 IU
Vitamin C	50 mcg	20 IU
Vitamin D (Cholecalciferol)	0.025 mcg	40,000 IU
Vitamin E (Natural)	0.67 mg	1.49 IU
Vitamin E (Synthetic)	0.9 mg	1.11 IU
Insulin	0.0347 mg	28.8 IU

Frequently Asked Questions

No. International Units (IU) are typically used for vitamins, hormones, and some enzymes. Minerals like Magnesium, Calcium, or Zinc are measured strictly by weight (mg or mcg) and do not have an IU equivalent.

Vitamin E comes in natural (d-alpha-tocopherol) and synthetic (dl-alpha-tocopherol) forms. The natural form is more biologically active, meaning 1 mg of natural Vitamin E provides more IU (activity) than 1 mg of the synthetic version. You must select the correct form for accuracy.

It depends entirely on the substance. 1000 IU of Vitamin D is a standard daily dose, whereas 1000 IU of Vitamin A is relatively small. Always consult Recommended Dietary Allowances (RDA) for context.

The standard conversion used is for pure crystalline insulin (approx 28.8 IU/mg). However, pharmaceutical preparations vary in concentration (e.g., U-100 insulin). Always use the concentration specified on the medication vial.