IU to mg Converter — mcg to IU & mg to IU Calculator
Use this free IU to mg converter to instantly convert International Units to milligrams, micrograms, and back. Supports Vitamin D, Vitamin A (retinol & beta-carotene), and Vitamin E (natural & synthetic). Bidirectional — type in either field.
IU to mg Converter
| IU | Vitamin D (mg) | Vit A Retinol (mg) | Vit E Natural (mg) |
|---|---|---|---|
| 100 IU | 0.0025 mg | 0.03 mg | 0.067 mg |
| 400 IU | 0.01 mg | 0.12 mg | 0.268 mg |
| 1,000 IU | 0.025 mg | 0.3 mg | 0.67 mg |
| 2,000 IU | 0.05 mg | 0.6 mg | 1.34 mg |
| 5,000 IU | 0.125 mg | 1.5 mg | 3.35 mg |
| 10,000 IU | 0.25 mg | 3.0 mg | 6.7 mg |
Important Medical Disclaimer
→ This IU to mg converter is for educational and informational purposes only.
→ IU conversion factors vary by substance. Always verify the conversion factor for your specific supplement or medication with a healthcare professional or pharmacist.
→ Do not adjust supplement or medication doses based solely on a conversion tool.
→ Sources: omnicalculator.com, mypharmatools.com, National Institutes of Health (NIH) Office of Dietary Supplements, WHO Technical Report Series
What is IU? A Simple Explanation
IU stands for International Unit — a unit of measurement used in pharmacology and nutrition to express the biological activity of a substance, rather than its mass or weight. Unlike milligrams (mg) or micrograms (mcg) which measure physical mass, an IU measures how much of a substance produces a defined biological effect in the body.
The IU was standardised by the World Health Organization (WHO) and is widely used for vitamins, hormones, vaccines, and medications whose biological potency matters more than their raw weight. This is why the IU to mg conversion varies by substance — 1 IU of Vitamin D is a different physical mass than 1 IU of Vitamin E, because the two vitamins have different biological potencies per gram.
Key fact: IU is NOT the same as mg or mcg.
You must know the substance to convert IU to mg. The same number of IU represents a different amount in milligrams for Vitamin D, Vitamin A, and Vitamin E.
IU to mg Conversion — How It Works
The IU to mg converter uses fixed conversion factors that have been established by the WHO and adopted in international pharmacopoeia standards. Each substance has its own conversion factor based on the biological activity of that vitamin per unit of mass.
Vitamin D — IU to mg
Therefore: 1,000 IU = 0.025 mg = 25 mcg | 40 IU = 1 mcg
Vitamin A — IU to mg
1 IU Vitamin A (Beta-carotene) = 0.0006 mg = 0.6 mcg
Vitamin E — IU to mg
1 IU Vitamin E (Synthetic, dl-alpha) = 0.45 mg
Why does IU conversion vary?
The IU to mg conversion varies because IU is based on biological activity, not mass. Natural vitamin E (d-alpha-tocopherol) is more biologically active per gram than synthetic vitamin E (dl-alpha-tocopherol) — so fewer milligrams of natural vitamin E are needed to equal 1 IU. Similarly, retinol has a different potency than beta-carotene, giving them different mcg to IU conversion factors.
IU to mg Conversion Tables
Vitamin D — IU to mg & mcg
| IU | mg | mcg | Common Use |
|---|---|---|---|
| 400 IU | 0.01 mg | 10 mcg | Standard daily supplement |
| 1,000 IU | 0.025 mg | 25 mcg | Common daily dose |
| 2,000 IU | 0.05 mg | 50 mcg | Higher maintenance dose |
| 4,000 IU | 0.1 mg | 100 mcg | Upper safe limit (IOM) |
| 5,000 IU | 0.125 mg | 125 mcg | Therapeutic dose |
| 10,000 IU | 0.25 mg | 250 mcg | Medical supervision only |
Vitamin A — IU to mcg (Retinol)
| IU | mg (Retinol) | mcg (Retinol) | Note |
|---|---|---|---|
| 500 IU | 0.15 mg | 150 mcg | Low dose |
| 1,000 IU | 0.3 mg | 300 mcg RAE | Children |
| 2,500 IU | 0.75 mg | 750 mcg RAE | Standard adult |
| 5,000 IU | 1.5 mg | 1,500 mcg RAE | RDA upper end |
| 10,000 IU | 3.0 mg | 3,000 mcg RAE | Upper tolerable limit |
Vitamin E — IU to mg (Natural vs Synthetic)
| IU | Natural (mg) | Synthetic (mg) |
|---|---|---|
| 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 |
Practical Examples — IU to mg Conversion
Example 1: 1000 IU Vitamin D to mg
- 1000 IU × 0.000025 = 0.025 mg of Vitamin D
- This equals 25 mcg — the same value shown on many EU supplement labels
- A typical 1000 IU Vitamin D tablet contains just 0.025 mg of the active compound
Example 2: 5000 IU Vitamin D to mcg
- 5000 IU × 0.025 = 125 mcg of Vitamin D
- This is a common high-dose supplement used for deficiency correction
Example 3: 400 IU Vitamin E (Natural) to mg
- 400 IU × 0.67 = 268 mg of natural d-alpha-tocopherol
- The same 400 IU of synthetic vitamin E = 400 × 0.45 = 180 mg
- This shows why the source (natural vs synthetic) matters for Vitamin E dosing
Example 4: 0.025 mg Vitamin D to IU (mcg to IU)
- 0.025 mg = 25 mcg of Vitamin D
- 25 mcg × 40 = 1,000 IU
- This is how EU labels showing 25 mcg correspond to 1000 IU on US labels
Why IU is Used on Supplement Labels
Understanding the IU to mg converter is particularly useful because supplement labels in different countries use different units. In the United States, Vitamin D labels traditionally show IU. In the European Union, labels often show mcg. Both refer to the same amount — knowing the mcg to IU conversion allows you to compare products accurately.
- 1,000 IU Vitamin D = 25 mcg — same supplement, different label conventions
- 400 IU Vitamin D = 10 mcg — the former standard RDA shown in two different units
- Vitamin E labels — must specify natural or synthetic, as the mg to IU factor differs significantly
- Vitamin A labels — may show RAE (Retinol Activity Equivalents) in mcg or IU depending on the country and product age
Sources & References
→ National Institutes of Health (NIH) — Office of Dietary Supplements: Vitamin D, Vitamin A, Vitamin E fact sheets
→ World Health Organization (WHO) — International Standards for vitamins and biological substances
→ Institute of Medicine (IOM) — Dietary Reference Intakes for Calcium and Vitamin D (2011)
→ omnicalculator.com, mypharmatools.com — IU conversion methodology reference