mcg to IU Converter
Created by: Daniel Hayes
Last updated:
For vitamin D, 1 mcg equals 40 IU, so multiply micrograms by 40: 25 mcg is 1,000 IU and 50 mcg is 2,000 IU. Other vitamins use different factors. Vitamin A as retinol is 3.33 IU per mcg, and vitamin E depends on whether it is natural or synthetic. Pick the vitamin below to convert in either direction.
mcg to IU Converter
ConversionConvert vitamin D, A and E between micrograms and International Units.
Vitamin D mcg to IU chart
IU = mcg × 40. This applies to both vitamin D2 (ergocalciferol) and D3 (cholecalciferol).
| Micrograms (mcg) | International Units (IU) |
|---|---|
| 5 mcg | 200 IU |
| 10 mcg | 400 IU |
| 12.5 mcg | 500 IU |
| 15 mcg | 600 IU |
| 20 mcg | 800 IU |
| 25 mcg | 1,000 IU |
| 50 mcg | 2,000 IU |
| 62.5 mcg | 2,500 IU |
| 75 mcg | 3,000 IU |
| 100 mcg | 4,000 IU |
| 125 mcg | 5,000 IU |
| 250 mcg | 10,000 IU |
| 500 mcg | 20,000 IU |
| 1,250 mcg | 50,000 IU |
Vitamin A (retinol)
| mcg RAE (retinol) | IU |
|---|---|
| 300 mcg | 1,000 IU |
| 600 mcg | 2,000 IU |
| 900 mcg | 3,000 IU |
| 1,500 mcg | 5,000 IU |
| 3,000 mcg | 10,000 IU |
Vitamin E
| IU | Natural (d-alpha) | Synthetic (dl-alpha) |
|---|---|---|
| 100 IU | 67 mg | 45 mg |
| 200 IU | 134 mg | 90 mg |
| 400 IU | 268 mg | 180 mg |
| 1,000 IU | 670 mg | 450 mg |
mcg to IU conversion factors
- Vitamin D: IU = mcg × 40. mcg = IU ÷ 40.
- Vitamin A, retinol: IU = mcg × 3.33. mcg = IU × 0.3.
- Vitamin A, supplemental beta-carotene: IU = mcg × 1.67. mcg = IU × 0.6.
- Vitamin E, natural: IU = mg × 1.49. mg = IU × 0.67.
- Vitamin E, synthetic: IU = mg × 2.22. mg = IU × 0.45.
A microgram is a fixed weight, one millionth of a gram. An International Unit is a measure of biological effect that was defined separately for each vitamin, which is why there is no single mcg to IU factor.
Worked examples
- A vitamin D3 softgel labeled 50 mcg: 50 × 40 = 2,000 IU.
- A prescription of 50,000 IU of vitamin D: 50,000 ÷ 40 = 1,250 mcg.
- A multivitamin with 900 mcg RAE of vitamin A from retinol: 900 ÷ 0.3 = 3,000 IU.
Frequently Asked Questions
How do I convert mcg to IU for vitamin D?
Multiply micrograms by 40. 25 mcg of vitamin D is 1,000 IU, 50 mcg is 2,000 IU and 125 mcg is 5,000 IU. To convert IU to mcg, divide by 40. The factor is the same for vitamin D2 and D3.
How many IU is 20 mcg of vitamin D?
20 mcg of vitamin D is 800 IU (20 × 40). That is the recommended daily amount for adults over 70 in the United States. Most adults up to age 70 need 15 mcg (600 IU).
Is the mcg to IU conversion the same for every vitamin?
No. An IU measures biological activity, so each vitamin has its own factor. Vitamin D is 40 IU per mcg, vitamin A as retinol is 3.33 IU per mcg, and vitamin E depends on whether it is natural (1 IU = 0.67 mg) or synthetic (1 IU = 0.45 mg).
Why do supplement labels now use mcg instead of IU?
The FDA’s updated Nutrition Facts and Supplement Facts rules require vitamin D and vitamin A in micrograms and vitamin E in milligrams. Manufacturers may still list IU in parentheses, which is why many labels show both, for example "25 mcg (1,000 IU)".
How do I convert vitamin A IU to mcg RAE?
For retinol (the form in most supplements and animal foods), multiply IU by 0.3 to get mcg RAE. 3,000 IU of retinol is 900 mcg RAE. For supplemental beta-carotene, multiply IU by 0.3 as well to get mcg RAE, but the weight of beta-carotene is twice that (1 IU = 0.6 mcg beta-carotene).
How do I convert vitamin E IU to mg?
Natural vitamin E (d-alpha-tocopherol): multiply IU by 0.67. Synthetic vitamin E (dl-alpha-tocopherol): multiply IU by 0.45. A 400 IU capsule is 268 mg if natural or 180 mg if synthetic. The label usually says which form it contains.
How much vitamin D is too much?
The upper limit for adults and children 9 and older is 100 mcg (4,000 IU) a day from all sources. Higher doses are sometimes prescribed to treat deficiency, but only under medical supervision.
Sources and References
- NIH Office of Dietary Supplements: Vitamin D fact sheet. 1 mcg = 40 IU; recommended intakes and upper limits.
- NIH Office of Dietary Supplements: Vitamin A fact sheet. IU to mcg RAE for retinol and beta-carotene.
- NIH Office of Dietary Supplements: Vitamin E fact sheet. IU to mg for natural and synthetic alpha-tocopherol.
- 21 CFR 101.9: Nutrition labeling of food. Units required on U.S. labels.
For general information only. Ask a doctor or pharmacist about the right dose for you.