Decode Your Vitamin Label in Seconds
Switch between IU, mcg, and mg for vitamins A, D, and E.
This tool was built by Serge (MSc) using established science and government sources. My academic background covers plant biology, environmental biology, and biogeochemistry. My tools are for educational purposes and give practical guidance, not professional advice.
A vitamin unit converter solves a small but annoying problem: supplement labels do not agree on units. Older bottles list IU, newer ones list mcg or mg, and the same vitamin ends up with two very different numbers.
Pick the vitamin, choose a direction, and type the amount from your label.
Why vitamin D is simple and A and E are not
Vitamin D has one fixed rate. One IU is 0.025 mcg, so 40 IU make 1 mcg, and it makes no difference whether the label says D2 or D3.
Vitamin A and vitamin E work differently. An IU measures biological activity, not weight, so the weight behind one IU changes with the form of the vitamin.
That is why the converter asks which form you have. Retinol and beta-carotene carry different factors for vitamin A, and natural and synthetic vitamin E do as well.
Three examples to try
A bottle that says 2,000 IU of vitamin D holds 50 mcg.
A capsule with 5,000 IU of retinol works out to 1,500 mcg RAE of vitamin A.
400 IU of natural vitamin E is 268 mg of alpha-tocopherol, while 400 IU of the synthetic form is 180 mg.
Common vitamin D amounts
| IU | mcg |
|---|---|
| 400 | 10 |
| 600 | 15 |
| 800 | 20 |
| 1,000 | 25 |
| 2,000 | 50 |
| 4,000 | 100 |
For reference, the NIH lists 600 IU (15 mcg) as the average daily amount for most adults.
Where a converter can mislead you
The factors are standard, but products are not. Vitamin E is often sold as an ester such as acetate, which weighs more than the plain form, so a milligram figure printed by the maker can differ from a conversion.
When a label already lists both units, trust the label. This tool is for the times it shows only one.
Once you have the unit you need, the Daily Value (%DV) Calculator shows how the amount compares with the daily reference, and Study Dose vs Product Dose checks it against what research used. If you are choosing between bottles, the Cost Per Dose Calculator puts a price on each serving, and the Upper Limit Checker adds up the same vitamin across every product you use.
Keep in mind that the amount on a label is not the amount your body absorbs. The Bioavailability Calculator looks at what helps each supplement absorb, and the Nutrient Gap Estimator shows where an eating pattern may commonly fall short.
Where the numbers come from
The conversion factors follow the FDA guidance on converting units of measure for vitamins A, D, and E on Nutrition and Supplement Facts labels.
Vitamin D amounts in both units are listed in the NIH Office of Dietary Supplements fact sheet on vitamin D.
This converter is for general education only and is not medical or professional advice. Always check product labels and speak with a qualified professional before making decisions about supplements.