About

In pharmacology, the International Unit (IU) is a measure of biological activity, not mass. This fundamental difference means there is no single conversion factor for converting IU to milligrams (mg). The relationship depends entirely on the potency and molecular weight of the specific substance. For instance, 1000 IU of Vitamin D3 has a completely different mass than 1000 IU of Vitamin A.

This tool is designed for pharmacists, lab technicians, and patients managing supplements. To prevent critical dosing errors, the interface restricts input until a specific substance is identified. It uses a database of standard biological equivalents accepted by the WHO and major pharmacopoeias. Accuracy in this conversion is vital; confusing Retinol with Beta-carotene equivalents, for example, can lead to overdosing or ineffective treatment.

Formulas

The formula requires a substance-specific conversion factor (k). The mass in milligrams is the product of the potency in IU and this biological equivalent factor.

m_mg = P_IU × k

Where k represents the mass per unit of potency defined by international standards (e.g., k = 0.0003 for Retinol).

Reference Data

Substance	1 IU Equivalent (mg)	Example Conversion (1000 IU)
Vitamin A (Retinol)	0.0003 mg	0.3 mg
Vitamin A (Beta-carotene)	0.0006 mg	0.6 mg
Vitamin D3 (Cholecalciferol)	0.000025 mg	0.025 mg
Vitamin E (Natural / d-alpha)	0.67 mg	670 mg
Vitamin E (Synthetic / dl-alpha)	0.9 mg	900 mg
Insulin (Human)	0.0347 mg	34.7 mg

Frequently Asked Questions

Because "IU" is not a unit of weight. Converting IU to mg without knowing the substance is mathematically impossible and medically dangerous. A generic conversion does not exist.

Natural Vitamin E (d-alpha-tocopherol) is more biologically active than synthetic Vitamin E (dl-alpha-tocopherol). Therefore, you need less mass (mg) of the natural form to achieve the same IU potency. This tool accounts for that specific difference.

Vitamin C is typically measured directly in milligrams (mg), not IU. While some older labels might use IU, modern standards rely on mass. This tool focuses on substances where IU is the primary measure (Vitamins A, D, E, Insulin).

The factor used (1 IU = 0.0347 mg) is for pure crystalline human insulin. Commercial insulin preparations are standardized, but always consult the specific package insert for clinical dosing, as formulations vary.