Dosage Converter Tool
Convert between IU, mcg, mg, and g. IU conversions use NIH-sourced factors specific to each vitamin.
How we calculate this
Standard metric conversions use universal factors: 1 g = 1,000 mg, 1 mg = 1,000 mcg.
IU (International Unit) conversions are vitamin-specific. We use factors from the NIH Office of Dietary Supplements:
- Vitamin D: 1 IU = 0.025 mcg (40 IU = 1 mcg)
- Vitamin A (retinol): 1 IU = 0.3 mcg RAE (3.33 IU = 1 mcg)
- Vitamin E (alpha-tocopherol): 1 IU = 0.67 mg (1.49 IU = 1 mg)
Sources
- NIH Office of Dietary Supplements — Vitamin D Fact Sheet: ods.od.nih.gov
- NIH Office of Dietary Supplements — Vitamin A Fact Sheet: ods.od.nih.gov
- NIH Office of Dietary Supplements — Vitamin E Fact Sheet: ods.od.nih.gov
Limitations
- IU conversions are currently supported for Vitamin D, Vitamin A (retinol), and Vitamin E only.
- Vitamin A conversion uses retinol equivalents (RAE). Beta-carotene uses a different factor.
- Vitamin E conversion uses natural d-alpha-tocopherol. Synthetic (dl-alpha) has a different factor.
- This tool converts units only — it does not recommend any dosage amount.
FAQs
What is an IU (International Unit)?
An IU is a standardized measurement used for vitamins and other substances. The actual weight (in mcg or mg) that 1 IU represents varies depending on the vitamin. For example, 1 IU of Vitamin D equals 0.025 mcg, while 1 IU of Vitamin A equals 0.3 mcg.
Why does IU conversion differ by vitamin?
IU is based on the biological activity of a substance, not its weight. Different vitamins have different molecular weights and potencies, so the conversion factor between IU and weight units (mcg or mg) is specific to each vitamin.
What is the difference between mcg and mg?
A microgram (mcg) is 1/1,000 of a milligram (mg). So 1 mg = 1,000 mcg. This is a standard metric conversion that applies to all substances.
Are these conversion factors accurate?
Yes. The IU-to-weight conversion factors used here are from the NIH Office of Dietary Supplements. Standard metric conversions (mg ↔ mcg, g ↔ mg) follow universal metric system rules.
Can I use this for all vitamins and supplements?
IU conversions are currently available for Vitamin D, Vitamin A (retinol), and Vitamin E (alpha-tocopherol). Standard metric conversions (mg, mcg, g) work for any substance.
Is this medical advice?
No. This tool converts units for informational purposes only. It does not recommend any dosage. Always follow the directions on your product label or your healthcare provider’s guidance.