IU (International Unit) is a standardized measure of biological activity used for vitamins, hormones, enzymes, and certain biologic products. It does not directly measure mass (mg or mcg). Each substance has its own IU-to-mass relationship based on its defined potency.

Why do we use IU instead of mg for some vitamins and biologics?

Different formulations of the same vitamin or biologic can have different strengths per milligram. IU measures biological effect rather than simple weight, so 1 IU of a properly standardized substance should deliver the same biological activity regardless of brand or form.

How do I convert IU to mcg or mg with this calculator?

To convert IU to mass you need the potency in IU per microgram (IU/µg). The calculator loads presets for common vitamins like Vitamin D and Vitamin A and lets you edit the IU/µg value for custom products. Once potency is set, enter either IU or mass and the tool instantly calculates the corresponding mcg, mg, or g.

How much is 1 IU to mg for Vitamin D?

For Vitamin D (D₂ or D₃), 1 IU is defined as 0.025 µg, which equals 0.000025 mg. This corresponds to 40 IU per microgram (IU/µg = 40). The calculator includes this as a preset so you can quickly convert common Vitamin D doses.

How many IU are in 1 mg of Vitamin D?

Because 1 µg of Vitamin D equals 40 IU and 1 mg = 1000 µg, 1 mg of Vitamin D is equal to 40,000 IU. Selecting the Vitamin D preset and entering 1 mg in the calculator will show this conversion automatically.

Is the IU to mg / mcg calculator medical advice?

No. This tool is for informational and educational purposes only. It uses standard reference values and user-provided potency, but it cannot verify your product’s labeling or your personal health needs. Always follow your product label and consult a qualified healthcare professional or pharmacist before making any dosing decisions.

IU to mg

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IU to mg

Trusted IU to mg & mcg conversions with editable potency, clear formulas, and intuitive UI.

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