IU to mg Calculator
Convert International Units (IU) into milligrams (mg) for common vitamins. Select the nutrient first, because IU conversion depends on the substance.
What does IU mean, and why convert IU to mg?
IU stands for International Unit. Unlike mg (milligrams), IU is not a fixed mass. IU measures biological activity, and that activity is different for each nutrient. That means there is no universal IU-to-mg formula that works for everything.
For example, 1,000 IU of vitamin D and 1,000 IU of vitamin E are not the same mass in mg. You must choose the right vitamin and, in some cases, the right chemical form.
Quick conversion factors used in this calculator
| Nutrient/Form | IU to mg factor | Equivalent in mcg |
|---|---|---|
| Vitamin D (D2/D3) | 1 IU = 0.000025 mg | 1 IU = 0.025 mcg |
| Vitamin A (Retinol) | 1 IU = 0.0003 mg | 1 IU = 0.3 mcg |
| Vitamin A (Beta-carotene) | 1 IU = 0.0006 mg | 1 IU = 0.6 mcg |
| Vitamin E (Natural d-alpha-tocopherol) | 1 IU = 0.67 mg | 1 IU = 670 mcg |
| Vitamin E (Synthetic dl-alpha-tocopherol) | 1 IU = 0.45 mg | 1 IU = 450 mcg |
How to use this IU to mg calculator
- Enter your supplement amount in IU.
- Select the correct nutrient and form from the dropdown.
- Click Calculate to see mg and mcg values.
- Use Reset to clear the form and start over.
Example 1: Vitamin D
If you enter 2,000 IU of vitamin D, the result is:
- 0.05 mg
- 50 mcg
Example 2: Vitamin E (natural)
If you enter 100 IU of natural vitamin E:
- 67 mg
- 67,000 mcg
Important notes before converting doses
1) IU is nutrient-specific
Never apply one vitamin’s IU conversion to another vitamin. This is a common dosing mistake.
2) Form matters
Vitamin E conversion changes between natural and synthetic forms. Vitamin A conversion also differs between retinol and beta-carotene.
3) Label units may vary
Modern supplement labels often use mcg or mg instead of IU. This calculator helps you compare old and new units clearly.
IU to mg formula
The formula is simple once the nutrient is known:
mg = IU × conversion factor
Then, to get micrograms:
mcg = mg × 1000
Frequently asked questions
Can I convert IU to mg without selecting a vitamin?
No. IU is based on biological potency, so each nutrient has a unique conversion factor.
Is higher IU always better?
Not necessarily. Dosing should match your health goals, lab results, and medical guidance. More is not always safer.
Why include mcg if this is an IU to mg calculator?
Because many supplement labels and clinical recommendations use mcg, seeing both units makes interpretation easier.