International units measure biological activity rather than weight, so the conversion is different for every vitamin and even for different forms of the same vitamin. US labels now use mcg or mg, while many supplements still show IU.
How to use the mcg to IU Converter
- Vitamin and form
- Amount in mcg (mg for vitamin E)
- Every result field is editable: type into Amount in IU and Amount in mcg (mg for vitamin E) plus every other field update to match.
Results update as you type, and every field accepts the units shown in its menu.
How it works
Choose the vitamin and form, then enter the amount in mcg (or mg for vitamin E); type in the IU result to convert the other way.
Inputs explained
| Field | What to enter |
|---|---|
| Vitamin and form | Choose one: Vitamin D (D2 or D3), Vitamin A – retinol, Vitamin A – beta-carotene supplement, Vitamin E – natural (d-alpha), per mg … |
| Amount in mcg (mg for vitamin E) | A number |
Example values
How the main result changes when Amount in mcg changes and everything else stays at the example values above:
| Amount in mcg (mg for vitamin E) | Amount in IU (IU) |
|---|---|
| 12.5 | 500 |
| 18.75 | 750 |
| 25 | 1,000 |
| 31.25 | 1,250 |
| 37.5 | 1,500 |
| 50 | 2,000 |
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
Vitamin D: 1 mcg = 40 IU
Vitamin A: 1 mcg retinol = 3.33 IU; 1 mcg beta-carotene (supplement) = 1.67 IU
Vitamin E: 1 mg d-alpha-tocopherol (natural) = 1.49 IU; 1 mg dl-alpha-tocopherol (synthetic) = 2.22 IU
Worked example
Inputs — Vitamin and form: Vitamin D (D2 or D3); Amount in mcg (mg for vitamin E): 25.
Results — Amount in IU = 1,000 IU.
Key terms
- IU
- International unit.
Frequently asked questions
How many IU is 25 mcg of vitamin D?
1,000 IU.
How many IU is 900 mcg of vitamin A?
3,000 IU as retinol.
Why do natural and synthetic vitamin E differ?
Synthetic vitamin E is a mixture of forms, only some of which are active.