Vitamin Unit Converter (IU to mcg and mg)
Choose the vitamin and form, then enter the amount in IU.
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Vitamin Unit Converter (IU to mcg and mg) by TheCalcTools
How the Vitamin Unit Converter (IU to mcg and mg) works
International units measure biological activity, so the conversion depends on the vitamin and its form. Vitamin D: 1 IU = 0.025 mcg (40 IU = 1 mcg). Vitamin A as retinol: 1 IU = 0.3 mcg RAE; beta-carotene from supplements: 1 IU = 0.15 mcg RAE. Vitamin E: 1 IU = 0.67 mg (natural) or 0.45 mg (synthetic).
US labels switched from IU to mcg and mg for these vitamins, so older and newer products may list different units.
The formula
Worked example
Using the default values shown in the calculator:
| Vitamin and form | Vitamin D (D2 or D3) |
|---|---|
| Amount (IU) | 1000 |
- 1000 IU of vitamin D = 25 mcg.
Result:
| Converted amount | 25 mcg |
|---|---|
| Factor per IU | 0.025 |
| Adult reference intake | Vitamin D: 15 mcg (600 IU) a day for most adults |
Frequently asked questions
How many mcg is 1000 IU of vitamin D?
25 mcg.
Is more vitamin D better?
No. The tolerable upper intake for most adults is 100 mcg (4,000 IU) a day unless a doctor advises otherwise.
Sources and further reading
- NIH Office of Dietary Supplements: Fact sheets (unit conversions)
- NIH ODS: Vitamin D fact sheet for health professionals
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This calculator gives general estimates for information and education. It is not medical advice and does not diagnose anything. Talk to a qualified health professional about your own situation. See our disclaimer.