How many mcg are in 1,000 IU of vitamin D?

For vitamin D, 1 IU equals 0.025 mcg, so 1,000 IU equals 25 mcg.

How many mg are in 1,000 IU of vitamin D?

1,000 IU of vitamin D equals 25 mcg, or 0.025 mg. Divide micrograms by 1,000 to get milligrams. This vitamin D conversion does not apply to vitamins A or E.

How do I convert mg or mcg back to IU?

Select the vitamin and its form, choose mg or mcg, then enter the amount in the right-hand field. For example, 0.025 mg or 25 mcg of vitamin D equals 1,000 IU. Each vitamin and form has its own factor.

Is the IU conversion the same for every vitamin?

No. An IU measures biological activity, so the factor depends on the vitamin and sometimes its form. Select the nutrient and form before converting.

Why does vitamin E default to mg instead of mcg?

Current U.S. Supplement Facts labels express vitamin E as milligrams of alpha-tocopherol. You can also select mcg in this calculator. Natural and synthetic vitamin E use different IU conversion factors.

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IU to mcg and mg converter

Convert International Units to micrograms (mcg) or milligrams (mg)—and back to IU. Select vitamin D, A, or E and its form before comparing amounts.

1,000 IU = 25 mcg

Vitamin D: 1 IU = 0.025 mcg.

Common vitamin D conversions

Vitamin D uses the same factor for D2 and D3: 1 IU equals 0.025 mcg, or 0.000025 mg. For example, 1,000 IU = 25 mcg = 0.025 mg. These are unit conversions, not recommended doses.

Comparing bottles? See three real vitamin D labels compared by unit and serving size.

Vitamin D (IU)	Vitamin D (mcg)	Vitamin D (mg)
400 IU	10 mcg	0.01 mg
600 IU	15 mcg	0.015 mg
800 IU	20 mcg	0.02 mg
1,000 IU	25 mcg	0.025 mg
2,000 IU	50 mcg	0.05 mg
4,000 IU	100 mcg	0.1 mg

IU is not a universal mass unit.

An International Unit represents biological activity, not a fixed weight. That is why 1 IU of vitamin D, vitamin A, and vitamin E converts differently.

The converter uses the U.S. label factors described by the NIH Office of Dietary Supplements:

Vitamin D: 1 IU = 0.025 mcg = 0.000025 mg.
Vitamin A (retinol or supplemental beta-carotene): 1 IU = 0.3 mcg RAE = 0.0003 mg RAE.
Vitamin E (natural d-alpha-tocopherol): 1 IU = 670 mcg alpha-tocopherol = 0.67 mg alpha-tocopherol.
Vitamin E (synthetic dl-alpha-tocopherol): 1 IU = 450 mcg alpha-tocopherol = 0.45 mg alpha-tocopherol.

For vitamin A, RAE means retinol activity equivalents; it is not the weight of beta-carotene. These factors do not apply to carotenoids in food. For vitamin E, the result expresses alpha-tocopherol activity for labeling, not the weight of the entire compound.

For vitamin A or E, check the form printed on the product label before using a factor. A unit conversion says nothing about whether that amount is appropriate for you.

IU conversion questions

How many mcg are in 1,000 IU of vitamin D?: For vitamin D, 1 IU equals 0.025 mcg, so 1,000 IU equals 25 mcg.
How many mg are in 1,000 IU of vitamin D?: 1,000 IU of vitamin D equals 25 mcg, or 0.025 mg. Divide micrograms by 1,000 to get milligrams. This vitamin D conversion does not apply to vitamins A or E.
How do I convert mg or mcg back to IU?: Select the vitamin and its form, choose mg or mcg, then enter the amount in the right-hand field. For example, 0.025 mg or 25 mcg of vitamin D equals 1,000 IU. Each vitamin and form has its own factor.
Is the IU conversion the same for every vitamin?: No. An IU measures biological activity, so the factor depends on the vitamin and sometimes its form. Select the nutrient and form before converting.
Why does vitamin E default to mg instead of mcg?: Current U.S. Supplement Facts labels express vitamin E as milligrams of alpha-tocopherol. You can also select mcg in this calculator. Natural and synthetic vitamin E use different IU conversion factors.

The number is only one part of the label.

Scan the full Supplement Facts panel with SuppLens to review serving size, nutrient forms, and other ingredients together.