IU to mg Converter (Vitamin A, E and D)

How it works

Vitamin A: 1 IU retinol = 0.3 mcg RAE; 1 IU supplemental beta-carotene = 0.15 mcg RAE; 1 IU dietary beta-carotene = 0.05 mcg RAE · Vitamin E: 1 IU natural = 0.67 mg; 1 IU synthetic = 0.45 mg alpha-tocopherol · Vitamin D: 1 IU = 0.025 mcg

An International Unit measures biological activity, not weight, so the factor depends on the vitamin and its chemical form. Since the 2016 FDA labeling rule, US labels show vitamin A in mcg RAE (retinol activity equivalents), vitamin E in mg of alpha-tocopherol and vitamin D in mcg, often with IU in brackets. Retinol is fully active, beta-carotene less so, and synthetic dl-alpha-tocopherol has only about half the activity of the natural d-form — which is why the same number of IU can mean very different weights.

Worked example

5,000 IU of vitamin A as retinol (retinyl palmitate) × 0.3 = 1,500 mcg RAE, which is 1.5 mg — well above the adult RDA of 700–900 mcg and half the 3,000 mcg upper limit for preformed vitamin A.

Sources: NIH Office of Dietary Supplements — Vitamin A and carotenoids fact sheet · NIH Office of Dietary Supplements — Vitamin E fact sheet · NIH Office of Dietary Supplements — Vitamin D fact sheet

Frequently asked questions