How the calculation works
mcg vitamin D = IU ÷ 40
A worked example
1,000 IU of vitamin D equals 25 mcg. A 2,000 IU label describes 50 mcg, and a 400 IU label describes 10 mcg.
Why vitamin D uses two units
Micrograms describe mass; International Units describe activity. Vitamin D has a defined relationship between the two, so a label can show both without describing two separate ingredients.
IU to mcg conversion table for vitamin D
These are equivalent amounts, not suggested doses.
| IU | mcg |
|---|---|
| 400 | 10 |
| 600 | 15 |
| 800 | 20 |
| 1,000 | 25 |
| 2,000 | 50 |
| 4,000 | 100 |
| 5,000 | 125 |
Common questions
Does this work for vitamin D3 and D2?
Yes. For vitamin D label conversions, 1 mcg equals 40 IU for either form.
Does this work for vitamin A or E?
No. IU conversion factors depend on the vitamin and sometimes its form. Do not use the vitamin D factor for other nutrients.
Is this a vitamin D blood test calculator?
No. Supplement amounts in IU or mcg differ from blood concentrations such as ng/mL or nmol/L. Ask your clinician to interpret a blood result.
Reference: NIH Office of Dietary Supplements: vitamin D. Reviewed .