Convert vitamins A and E between metric units (mcg/mg) and International Units (IU) using FDA conversion factors. Each vitamin has its own factor, and both vitamin A and vitamin E also differ by form. Vitamin K has no IU, so there is nothing to convert. For vitamin D, see our dedicated D converter.
Convert
1 IU retinol = 0.3 mcg RAE, so 1 mcg RAE = 3.33 IU
Vitamin A activity: 900 mcg RAE
Conversion factors by vitamin and form
| Vitamin / Form | FDA conversion | RDA reference |
|---|---|---|
| Vitamin A, retinol (preformed) | 1 IU = 0.3 mcg RAE, so 1 mcg RAE = 3.33 IU | Men 900 mcg RAE; Women 700 mcg RAE |
| Vitamin A, beta-carotene (supplement in oil) | 1 IU = 0.6 mcg; 2 mcg = 1 mcg RAE = 3.33 IU | 2:1 conversion to retinol activity |
| Vitamin A, beta-carotene (food) | 1 IU = 0.6 mcg; 12 mcg = 1 mcg RAE = 20 IU | 12:1 conversion to retinol activity |
| Vitamin E, natural d-alpha-tocopherol | 1 IU = 0.67 mg, so 1 mg = 1.49 IU | 15 mg adults (22.4 IU natural) |
| Vitamin E, synthetic dl-alpha-tocopherol | 1 IU = 0.45 mg on the label, so 1 mg = 2.22 IU | 15 mg adults (33.3 IU synthetic) |
| Vitamin K (K1, MK-4, MK-7) | No IU exists; labels list mcg | Men 120 mcg; Women 90 mcg (AI) |
Important: vitamin A is a “RAE” unit, not just mcg
Modern vitamin A labels use mcg RAE (Retinol Activity Equivalents). This accounts for the fact that beta-carotene (plant source) converts to retinol at different efficiencies. The IU system pre-dated RAE and did not distinguish the source, which is why old IU values can be confusing:
- Pre-2020 label “5,000 IU vitamin A” equals 1,500 mcg RAE if the source was retinol or purified beta-carotene in a supplement, but only 250 mcg RAE if it was beta-carotene from food (FDA: 0.3 vs 0.05 mcg RAE per IU).
- Modern label “900 mcg RAE” is unambiguous: that’s the absorbed retinol activity, regardless of source.
- The Upper Limit (UL) for adults is 3,000 mcg RAE/day of preformed vitamin A (retinol and retinyl esters, from animal foods and many supplements). Beta-carotene has no UL.
Vitamin E: natural vs synthetic matters
Vitamin E supplements come in two forms with different conversion factors:
- Natural d-alpha-tocopherol (RRR-alpha-tocopherol, from sunflower or soybean oil): 1 IU = 0.67 mg, so 1 mg = 1.49 IU. The “d-” prefix is the natural isomer.
- Synthetic dl-alpha-tocopherol (all-rac-alpha-tocopherol): 1 IU = 0.45 mg of alpha-tocopherol on the label, so 1 mg on the label = 2.22 IU. The “dl-” prefix means a mix of eight stereoisomers, and only half of them (the 2R forms) count toward the label amount. The synthetic compound itself therefore weighs about twice what the label shows: 1 IU is about 0.9 mg of dl-alpha-tocopherol.
- Practical implication: A “400 IU vitamin E” supplement lists about 268 mg of alpha-tocopherol if natural, or 180 mg if synthetic. Same IU, different mg on the bottle.
- Modern labels (post-2020 FDA): mg of alpha-tocopherol, where 1 mg = 1 mg RRR-alpha-tocopherol = 2 mg all-rac-alpha-tocopherol. Ester forms (acetate, succinate) use the same IU factors as their natural or synthetic parent.
Vitamin K1 vs K2 (and why MK-7 is special)
Vitamin K has no International Unit. US labels list vitamin K in mcg, and FDA’s 2019 unit-conversion guidance covers only folate, niacin and vitamins A, D and E, so there is no mcg-to-IU factor to apply. Compare vitamin K products in mcg. The forms do differ in bioavailability and half-life:
- Vitamin K1 (phylloquinone): from leafy greens, primarily activates coagulation factors. Short half-life (~1-2 hours).
- Vitamin K2 MK-4 (menatetrenone): short half-life (~1 hour). Used in some bone-health studies at high pharmacological doses (45 mg/day).
- Vitamin K2 MK-7 (long-chain menaquinone, from natto): half-life ~72 hours. The form used in most modern bone-health trials at 90-180 mcg/day. Much more efficient bioavailability than MK-4.
Sources and corrections
Conversion factors come from FDA, Converting Units of Measure for Folate, Niacin, and Vitamins A, D, and E on the Nutrition and Supplement Facts Labels: Guidance for Industry (August 2019), Tables 2, 3, 5 and 6.
Correction, October 16, 2026: an earlier version of this converter used 12 mcg = 3.33 IU for beta-carotene from food (the correct value is 20 IU, because 1 IU = 0.6 mcg of beta-carotene from any source) and offered a 1:1 IU factor for vitamin K, which does not exist. We also made clear that the synthetic vitamin E factor applies to mg of alpha-tocopherol on the label.