BIPM-ratified constants · v1.0

Converter

Vitamin, a converter (iu ↔ mcg rae) calculator.

Convert vitamin A IU to mcg RAE or mcg RAE to IU using source-specific factors for retinol, supplemental, and dietary beta-carotene.

From

retinol / retinyl esters

retinol

3000 retinol =900Converted Vitamin A Amount

Equivalents

Precision: 6 dp · Notation: Decimal · 2 units

→ mcg RAE

IUiu_to_rae900

RAE → IU

mcgrae_to_iu10,000

Common pairings

1 retinolequals0.3 iu_to_rae

1 retinolequals3.3333 rae_to_iu

1 supplemental_bcequals0.3 iu_to_rae

1 supplemental_bcequals3.3333 rae_to_iu

1 dietary_bcequals0.05 iu_to_rae

1 dietary_bcequals20 rae_to_iu

1 other_carotenoidsequals0.025 iu_to_rae

1 other_carotenoidsequals40 rae_to_iu

The conversion

How the value
is computed.

Understanding Vitamin A Units: IU vs. mcg RAE

Vitamin A appears on food labels, supplement facts panels, and clinical reports in two distinct measurement systems: International Units (IU) and micrograms of Retinol Activity Equivalents (mcg RAE). Because the body absorbs and converts different forms of vitamin A with vastly different efficiencies, a single numeric unit cannot accurately represent all sources. This vitamin A converter applies source-specific conversion factors endorsed by federal health authorities to deliver precise, clinically meaningful results.

Why Two Different Units Exist

The International Unit served as the dominant measurement for fat-soluble vitamins throughout most of the 20th century. An IU of vitamin A was defined as the biological activity of 0.3 micrograms of retinol. That definition obscured a critical biochemical reality: dietary beta-carotene from plant foods is absorbed and converted to retinol far less efficiently than either preformed retinol or supplemental beta-carotene in oil-based capsules.

In 2001, the Institute of Medicine (now the National Academy of Medicine) introduced Retinol Activity Equivalents to replace the older Retinol Equivalents (RE) standard and to better reflect measured bioavailability data. According to the NIH Office of Dietary Supplements Vitamin A Health Professional Fact Sheet, the RAE system directly accounts for the lower intestinal conversion efficiency of provitamin A carotenoids from food. The U.S. Food and Drug Administration mandated the use of mcg RAE on updated Nutrition and Supplement Facts labels starting in 2020, as detailed in the FDA guidance on Converting Units of Measure for Folate, Niacin, and Vitamins A, D, and E.

The Conversion Formula and Source Factors

The core formula for converting IU to mcg RAE is:

mcg RAE = IU × f_source

The conversion factor f varies by the chemical form of vitamin A being measured. Four distinct values apply:

Preformed retinol (f = 0.3): Found in animal-derived foods such as liver, dairy products, and eggs, as well as in most retinol-based multivitamin supplements. One IU of retinol equals exactly 0.3 mcg retinol, which equals 0.3 mcg RAE.
Supplemental beta-carotene (f = 0.3): Beta-carotene in oil-based supplement form is highly bioavailable. Each IU of supplemental beta-carotene represents 0.6 mcg of the compound. Because 2 mcg of supplemental beta-carotene yields 1 mcg RAE, the factor equals 0.6 ÷ 2 = 0.3 mcg RAE per IU.
Dietary beta-carotene (f = 0.05): Beta-carotene embedded in plant food matrices faces significant absorption barriers. Each IU of dietary beta-carotene represents 0.6 mcg of the compound, but because 12 mcg of dietary beta-carotene is required to yield 1 mcg RAE, the factor equals 0.6 ÷ 12 = 0.05 mcg RAE per IU.
Other provitamin A carotenoids (f = 0.025): Alpha-carotene and beta-cryptoxanthin convert to retinol even less efficiently than dietary beta-carotene. Each IU represents 0.6 mcg; since 24 mcg is required per mcg RAE, the factor equals 0.6 ÷ 24 = 0.025 mcg RAE per IU.

Worked Conversion Examples

Example 1 — Retinol supplement: A supplement label lists 5,000 IU of vitamin A as retinol. Applying f = 0.3: 5,000 × 0.3 = 1,500 mcg RAE. This is approximately 1.7 times the adult male RDA of 900 mcg RAE.

Example 2 — Supplemental beta-carotene: A high-dose capsule provides 25,000 IU of beta-carotene in oil. Using f = 0.3: 25,000 × 0.3 = 7,500 mcg RAE, which exceeds the adult Tolerable Upper Intake Level for preformed vitamin A.

Example 3 — Dietary beta-carotene: A nutrient database lists one cup of cooked sweet potato at approximately 38,433 IU of beta-carotene from food. Using f = 0.05: 38,433 × 0.05 = 1,922 mcg RAE, more than twice the adult RDA from a single serving.

Example 4 — Other provitamin A carotenoids: A food item provides 4,800 IU from alpha-carotene. Using f = 0.025: 4,800 × 0.025 = 120 mcg RAE.

Reverse Conversion: mcg RAE to IU

To convert from mcg RAE back to IU, divide by the source factor:

IU = mcg RAE ÷ f_source

The adult male RDA of 900 mcg RAE from retinol equals 900 ÷ 0.3 = 3,000 IU. The same 900 mcg RAE expressed as dietary beta-carotene equals 900 ÷ 0.05 = 18,000 IU — a six-fold difference that illustrates why specifying the vitamin A source is essential for any accurate conversion.

Clinical and Practical Applications

Accurate IU-to-RAE conversion matters in several real-world contexts: reconciling old supplement labels that used IU with new ones that list mcg RAE; calculating total daily vitamin A intake across mixed food and supplement sources; verifying that high-dose supplementation stays below the Tolerable Upper Intake Level of 3,000 mcg RAE of preformed vitamin A per day for adults; and updating legacy nutrient databases. Source-specific factors are published by the NIH Dietary Supplement Ingredient Database (DSID) and further corroborated by peer-reviewed analysis in published PMC research on beta-carotene IU-to-RAE conversions (PMC7373782).

Reference

Frequently asked questions

What is the difference between IU and mcg RAE for vitamin A?

IU (International Unit) is a legacy measure of biological activity set to 0.3 mcg of retinol per unit, while mcg RAE (micrograms Retinol Activity Equivalents) reflects how much usable vitamin A the body actually obtains after absorption and conversion. Because preformed retinol, supplemental beta-carotene, and dietary beta-carotene are processed at very different efficiencies, the same IU number can represent vastly different amounts of bioavailable vitamin A. The RAE system, adopted by the National Academy of Medicine in 2001 and mandated on U.S. labels since 2020, corrects for these differences.

Why does the vitamin A conversion factor differ depending on the source?

The human intestine absorbs and cleaves provitamin A carotenoids far less efficiently than preformed retinol. Dietary beta-carotene from food is embedded in plant cell matrices that limit bioavailability — 12 mcg of dietary beta-carotene yields only 1 mcg RAE, compared to just 2 mcg of oil-based supplemental beta-carotene for the same result. Other carotenoids like alpha-carotene require 24 mcg per mcg RAE. These biological ratios translate directly into the conversion factors: 0.3 for retinol and supplemental beta-carotene, 0.05 for dietary beta-carotene, and 0.025 for other provitamin A carotenoids.

How do I convert 5,000 IU of vitamin A retinol to mcg RAE?

Multiply 5,000 IU by the retinol conversion factor of 0.3: 5,000 × 0.3 = 1,500 mcg RAE. This is the amount of biologically active vitamin A the body receives from 5,000 IU of preformed retinol, whether from food or supplements. For context, the adult RDA for vitamin A is 700 mcg RAE for women and 900 mcg RAE for men, so 5,000 IU of retinol provides approximately 1.7 to 2.1 times the daily requirement and approaches the Tolerable Upper Intake Level of 3,000 mcg RAE per day.

What is the recommended daily intake of vitamin A in mcg RAE?

According to the NIH Office of Dietary Supplements, the Recommended Dietary Allowance (RDA) for vitamin A is 700 mcg RAE per day for adult women and 900 mcg RAE per day for adult men. Pregnant women require 770 mcg RAE daily, while breastfeeding women need 1,300 mcg RAE. Children's RDAs range from 300 mcg RAE for ages 1–3 to 600 mcg RAE for ages 9–13. The Tolerable Upper Intake Level for preformed vitamin A is 3,000 mcg RAE per day for adults — a threshold relevant only to retinol and supplemental beta-carotene, not dietary carotenoids.

Why did nutrition labels switch from IU to mcg RAE for vitamin A?

The FDA updated Nutrition Facts and Supplement Facts label regulations, with compliance required by 2020, because IU values are misleading when comparing different vitamin A forms. A food rich in dietary beta-carotene can display a large IU number that substantially overstates its actual vitamin A activity, since only a fraction of food-derived carotenoids convert to retinol. Switching to mcg RAE gives consumers, clinicians, and researchers an accurate, source-adjusted measure of true vitamin A nutrition, improving dietary assessment accuracy and reducing risk of both chronic under-supplementation and toxic over-supplementation.

How do I convert mcg RAE back to IU for vitamin A?

Divide the mcg RAE value by the appropriate source factor: IU = mcg RAE ÷ f. For retinol or supplemental beta-carotene (f = 0.3), 900 mcg RAE ÷ 0.3 = 3,000 IU. For dietary beta-carotene (f = 0.05), 900 mcg RAE ÷ 0.05 = 18,000 IU. For other provitamin A carotenoids (f = 0.025), 900 mcg RAE ÷ 0.025 = 36,000 IU. The dramatic difference in IU values for the same RAE amount demonstrates precisely why the vitamin A source must always be specified when converting between these two unit systems.