Convert mcg to IU
Enter a microgram amount and choose the vitamin form. The calculator will convert your value to International Units (IU).
Important: IU conversions are nutrient-specific. The same mcg amount can produce very different IU values depending on vitamin type and chemical form.
What does mcg to IU mean?
mcg (micrograms) measures mass, while IU (International Units) measures biological activity. Because IU is based on activity, not weight alone, each vitamin has its own conversion factor. That is why there is no single universal “mcg to IU” formula for all supplements.
This is especially important for vitamin D, vitamin A, and vitamin E labels, where dosages may appear in either mcg or IU depending on the brand, country, and labeling standard.
Common mcg to IU conversion formulas
| Vitamin form | Formula (mcg → IU) | Example |
|---|---|---|
| Vitamin D (D2 / D3) | IU = mcg × 40 | 25 mcg = 1,000 IU |
| Vitamin A (retinol) | IU = mcg ÷ 0.3 | 900 mcg = 3,000 IU |
| Vitamin A (beta-carotene supplement) | IU = mcg ÷ 0.6 | 600 mcg = 1,000 IU |
| Vitamin A (beta-carotene from food) | IU = mcg ÷ 1.2 | 1,200 mcg = 1,000 IU |
| Vitamin E (natural d-alpha-tocopherol) | IU = mcg ÷ 670 | 670 mcg = 1 IU |
| Vitamin E (synthetic dl-alpha-tocopherol) | IU = mcg ÷ 450 | 450 mcg = 1 IU |
How to use this mcg to IU calculator
- Type your supplement amount in mcg.
- Select the exact nutrient form from the dropdown.
- Click Calculate IU to get your converted value instantly.
If you are converting vitamin A or vitamin E, choosing the correct form matters. Retinol and beta-carotene are not interchangeable, and natural vs synthetic vitamin E uses different conversion factors.
Practical examples
Vitamin D: If your label shows 50 mcg of vitamin D3, the equivalent is 2,000 IU.
Vitamin A: If your supplement has 300 mcg retinol, that equals 1,000 IU.
Vitamin E: If you have 6,700 mcg natural vitamin E, that equals 10 IU.
Tips to avoid conversion mistakes
- Always check whether your label lists retinol or beta-carotene for vitamin A.
- For vitamin E, confirm whether the source is natural d-alpha or synthetic dl-alpha.
- Do not assume one vitamin’s conversion factor applies to another vitamin.
- If dosing for a child, pregnancy, or medical condition, confirm with a licensed clinician.
FAQ
Is 1 mcg always the same number of IU?
No. IU depends on biological activity and the specific vitamin form.
Why do supplement labels switch between mcg and IU?
Regulations and labeling standards vary by region and year. Many newer labels now prefer mcg for vitamins like D, but IU still appears frequently.
Can I use this for medication decisions?
This tool is for educational and label-reading support. For treatment decisions, use your clinician’s recommendations and official product labeling.