Vitamin IU to mcg Converter
Convert International Units (IU) to micrograms (mcg) for vitamins A, D, and E.
Covers different forms of each vitamin.
Select a vitamin and form, then enter IU or mcg to convert.
Understanding Vitamin IU and mcg Conversions
International Units (IU) are a measurement of biological activity, not weight. The same number of IU can represent different weights depending on the vitamin and its chemical form. In 2016, the US FDA updated nutrition labeling to require vitamins to be listed in metric units (mcg or mg) instead of IU, but many supplement labels still show IU. This makes conversion essential for comparing products.
Vitamin D Conversions:
Vitamin D conversion is the same for both D2 (ergocalciferol) and D3 (cholecalciferol):
1 IU = 0.025 mcg
1 mcg = 40 IU
Common supplement doses:
| IU | mcg |
|---|---|
| 400 IU | 10 mcg |
| 600 IU | 15 mcg |
| 1,000 IU | 25 mcg |
| 2,000 IU | 50 mcg |
| 5,000 IU | 125 mcg |
| 10,000 IU | 250 mcg |
The recommended daily allowance (RDA) for adults is 600 IU (15 mcg), increasing to 800 IU (20 mcg) for adults over 70.
Vitamin A Conversions:
Vitamin A conversion depends on the form:
For retinol (preformed vitamin A, from animal sources):
1 IU = 0.3 mcg retinol = 0.3 mcg RAE
For beta-carotene (provitamin A, from plant sources):
1 IU from supplements = 0.3 mcg RAE
1 IU from food = 0.05 mcg RAE
RAE stands for Retinol Activity Equivalents, the modern standard unit.
Common supplement doses:
| IU (retinol) | mcg RAE |
|---|---|
| 2,500 IU | 750 mcg |
| 5,000 IU | 1,500 mcg |
| 10,000 IU | 3,000 mcg |
| 25,000 IU | 7,500 mcg |
The RDA for adult men is 900 mcg RAE (3,000 IU retinol). For adult women, it is 700 mcg RAE (2,333 IU retinol). The upper limit is 3,000 mcg RAE (10,000 IU retinol) per day.
Vitamin E Conversions:
Vitamin E has two common supplemental forms:
For d-alpha-tocopherol (natural vitamin E):
1 IU = 0.67 mg = 670 mcg
For dl-alpha-tocopherol (synthetic vitamin E):
1 IU = 0.45 mg = 450 mcg
Common supplement doses:
| IU (natural) | mg alpha-tocopherol |
|---|---|
| 100 IU | 67 mg |
| 200 IU | 134 mg |
| 400 IU | 268 mg |
| 800 IU | 536 mg |
| 1,000 IU | 670 mg |
The RDA for adults is 15 mg (22.4 IU natural). The upper limit is 1,000 mg (1,500 IU natural) per day.
Why the Conversion Is Not Simple:
IU was designed in the early 20th century to standardize the biological potency of vitamins before their chemical structures were fully understood. Different chemical forms of the same vitamin have different potencies per unit of weight, which is why IU values differ by form. The move to metric units (mcg, mg) aims to reduce this confusion.
Important: Always check which form of the vitamin is listed on your supplement label before converting. Using the wrong conversion factor can lead to significant errors in calculating your intake.