mcg to IU Converter
25 mcg of vitamin D equals 1,000 IU, but 25 mcg of vitamin A retinol equals 83.33 IU. This mcg to IU converter works only for the listed nutrient presets because International Units are substance specific. Pick the exact vitamin form on your label before you convert.
Quick answer
Vitamin D uses 1 mcg = 40 IU, which also means 1 IU = 0.025 mcg.
What this tells you
- •Vitamin D uses 1 mcg = 40 IU, which also means 1 IU = 0.025 mcg.
- •Vitamin A here means preformed retinol, where 1 IU = 0.3 mcg.
- •Vitamin E uses different factors for natural and synthetic forms, so the label form matters.
- •If your label uses mcg RAE, beta-carotene, or mg alpha-tocopherol, do not force it into the wrong preset.
How to Use
- 1Enter the amount you want to convert.
- 2Choose the direction, mcg to IU or IU to mcg.
- 3Pick the preset that matches the exact nutrient form on the label.
- 4Convert and compare the result with the unit shown on your bottle, chart, or paperwork.
How It Works
Formula
Vitamin D: IU = mcg ÷ 0.025 and mcg = IU × 0.025
Vitamin A (retinol): IU = mcg ÷ 0.3 and mcg = IU × 0.3
Vitamin E (natural): IU = mcg ÷ 670 and mcg = IU × 670
Vitamin E (synthetic): IU = mcg ÷ 450 and mcg = IU × 450International Units measure biological activity, not mass, so each nutrient form uses its own conversion factor. This tool assumes the amount you enter already matches the preset you selected on the label. It is for label-style unit conversion only, not for diagnosis, deficiency screening, or dosing advice.
Calculation note: values are processed in the order shown above, using the current input units.
Worked Examples
Convert 25 mcg of vitamin D to IU
Vitamin D uses 1 IU = 0.025 mcg, so 25 mcg divided by 0.025 equals 1,000 IU.
Convert 3,000 IU of vitamin A retinol to mcg
Vitamin A retinol uses 1 IU = 0.3 mcg, so 3,000 IU multiplied by 0.3 equals 900 mcg.
Convert 13,400 mcg of natural vitamin E to IU
Natural vitamin E uses 1 IU = 670 mcg, so 13,400 mcg divided by 670 equals 20 IU.
Common label conversions by preset
Quick lookups for the supported presets only.
| Preset | mcg | IU |
|---|---|---|
| Vitamin D | 10 mcg | 400 IU |
| Vitamin D | 25 mcg | 1,000 IU |
| Vitamin A (retinol) | 900 mcg | 3,000 IU |
| Vitamin E natural | 13,400 mcg | 20 IU |
| Vitamin E synthetic | 9,000 mcg | 20 IU |
Vitamin A beta-carotene, vitamin A in mcg RAE, and vitamin E labels shown in mg need different handling.
Common mistakes
- Using one factor for every vitamin. IU is substance specific, so vitamin D, vitamin A, and vitamin E do not share one conversion rule.
- Picking the vitamin A retinol preset when the label actually shows beta-carotene or mcg RAE.
- Mixing up natural and synthetic vitamin E, which use different IU factors.
Limitations
This tool only covers the listed supplement-style conversions: vitamin D, vitamin A as retinol, and vitamin E as either natural d-alpha-tocopherol or synthetic dl-alpha-tocopherol. It does not convert vitamin A carotenoids, mcg RAE, mg alpha-tocopherol, or prescription-specific dosing instructions. Rounded outputs are unit estimates only.