Convert mcg to IU, or IU to mcg, for vitamin D, vitamin A, vitamin E or insulin: pick the substance and enter the amount in mcg or mg.
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mcg to Units Formula
The following formula is used to convert micrograms to international units for a substance with a defined IU potency.
Variables:
- IU is the number of international units
- mcg is the amount in micrograms
- F is the number of micrograms per 1 IU for the selected substance
To convert mcg to IU, divide the amount in micrograms by the compound-specific mcg-per-IU factor. For example, vitamin D uses 0.025 mcg per IU, so 10 mcg of vitamin D equals 400 IU.
What is mcg to Units Conversion?
Micrograms (mcg) measure mass, while international units (IU) measure biological activity or potency. Because of that difference, there is no single universal conversion between mcg and IU. Each vitamin or medicine that uses IU has its own official potency definition, which determines how many micrograms equal 1 IU.
For example, vitamin D2 and vitamin D3 use 0.025 mcg per IU, retinol uses 0.3 mcg per IU, and traditional vitamin A IU use 0.6 mcg of all-trans beta-carotene mass per IU. Beta-carotene mass is not mcg RAE: dietary and supplemental sources have different RAE mappings. The pure-human-insulin reference uses 34.7 mcg per IU; it does not convert insulin analogues, solution volumes or syringe markings. See NIH vitamin A conversions and the WHO insulin reference report.
How to Calculate mcg to Units?
The following steps outline how to convert micrograms to international units.
- First, determine the amount in micrograms (mcg).
- Next, identify the substance being converted and find its mcg-per-IU factor.
- Then, divide the mcg value by the mcg-per-IU factor using the formula IU = mcg / F.
- Finally, verify the result with the calculator above.
mcg to Units Conversion Table
The table below shows arithmetic for a 10 mcg amount at each explicitly stated quantity basis; these are not dose recommendations. Vitamin E rows use the alpha-tocopherol nutrient-label amount. NIH label conversions use 670 mcg per natural-source IU and 450 mcg per synthetic-source IU; total synthetic ingredient mass is a different quantity. See NIH vitamin E labeling conversions.
| Substance | mcg per 1 IU | 10 mcg in IU |
|---|---|---|
| Vitamin D3 (cholecalciferol) | 0.025 mcg | 400 IU |
| Vitamin D2 (ergocalciferol) | 0.025 mcg | 400 IU |
| Vitamin A (retinol) | 0.3 mcg | 33.33 IU |
| Vitamin A (retinol activity equivalent) | 0.3 mcg RAE | 33.33 IU |
| Vitamin A (all-trans beta-carotene physical mass) | 0.6 mcg | 16.67 IU |
| Vitamin E (natural nutrient-label amount) | 670 mcg | 0.01493 IU |
| Pure human insulin reference | 34.7 mcg | 0.2882 IU |
| Vitamin E (synthetic nutrient-label amount) | 450 mcg | 0.02222 IU |
Example Problem
Use the following variables as an example problem to test your knowledge.
Amount = 10 mcg
Substance = Vitamin D3
Factor (F) = 0.025 mcg per IU
Using the formula: IU = mcg / F = 10 / 0.025 = 400 IU
