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IU Converter – Vitamin D, A and E from IU to µg or mg

Convert international units (IU) to micrograms or milligrams, and back, for vitamins D, A and E with this IU converter.

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For information only, not medical advice. Reference values describe healthy population groups and do not tell you what dose you should take. Ask a doctor, pharmacist or dietitian before starting, stopping or combining supplements, especially if you are pregnant, take medication or have a health condition.

Reference values are for adults aged 19 and over. Children have different, lower limits. Sources: US Dietary Reference Intakes (NIH Office of Dietary Supplements) and EFSA Dietary Reference Values and Tolerable Upper Intake Levels (2024). Reviewed October 7, 2026.

Runs in your browser – your data never leaves your device Also available via our free API

How to use the IU Converter

  1. 1 Choose the vitamin and its form, for example vitamin E as natural d-alpha-tocopherol.
  2. 2 Enter the value and choose whether to convert from IU to µg/mg or the other way round.
  3. 3 Read the converted amount; the conversion factor is shown below the result.

What is an international unit?

An international unit (IU, in Dutch IE) measures a vitamin by its biological activity rather than its weight. Because different forms of a vitamin have different activity, there is no single IU-to-milligram factor: each vitamin, and sometimes each form, has its own. US labels switched vitamins A, D and E from IU to µg or mg in 2020, and EU labels use µg or mg, but IU still appears on many products and in older advice.

Conversion factors

Vitamin and form 1 IU equals
Vitamin D (D3 or D2) 0.025 µg
Vitamin A as retinol 0.3 µg RAE
Vitamin A as beta-carotene from supplements 0.15 µg RAE
Vitamin E, natural (d-alpha-tocopherol) 0.67 mg
Vitamin E, synthetic (dl-alpha-tocopherol) 0.45 mg

In the other direction: 1 µg of vitamin D is 40 IU, 1 µg RAE of retinol is 3.33 IU and 1 mg of natural vitamin E is 1.49 IU.

Vitamin D

Vitamin D is the most common reason to convert. 400 IU is 10 µg, 1,000 IU is 25 µg, 2,000 IU is 50 µg and 4,000 IU is 100 µg – the adult upper limit. Use the vitamin D calculator to add up several sources and compare them with the reference values.

Vitamin A: retinol or beta-carotene?

Vitamin A on a label may be preformed vitamin A (retinol or retinyl esters) or beta-carotene, which the body converts to vitamin A as needed. The factors differ, and the upper limit applies only to preformed vitamin A, so check which form your product contains. Smokers are advised to avoid beta-carotene supplements.

Vitamin E: natural or synthetic?

Natural vitamin E (d-alpha-tocopherol, sometimes RRR-alpha-tocopherol) is more active than the synthetic dl-form (all-rac-alpha-tocopherol). 400 IU of natural vitamin E is 268 mg, while 400 IU of the synthetic form is 180 mg. The label usually states the form in brackets. Mixed tocopherols other than alpha-tocopherol do not count towards the reference values.

Sources

Frequently asked questions

How many mcg is 1,000 IU of vitamin D?

1,000 IU of vitamin D is 25 mcg (µg).

How many mg is 400 IU of vitamin E?

268 mg for natural vitamin E (d-alpha-tocopherol) and 180 mg for synthetic vitamin E (dl-alpha-tocopherol).

Why can I not convert IU for vitamin C or minerals?

International units are only used for vitamins A, D and E. Vitamin C, B vitamins and minerals are always measured by weight.

Is IU the same as IE?

Yes. IE (internationale eenheid) is the Dutch name for an international unit.

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