μg to IU Converter
Convert micrograms (μg) to International Units (IU) for vitamins and other substances. Select your vitamin type for accurate conversions between weight-based and biological activity measurements.
Conversion Factors
The conversion between micrograms and International Units varies depending on the specific substance. IU measures biological activity rather than weight, which is why different vitamins require different conversion factors.
| Substance | 1 μg equals | 1 IU equals |
|---|---|---|
| Vitamin D (D2 or D3) | 40 IU | 0.025 μg |
| Vitamin A (Retinol) | 3.33 IU | 0.3 μg |
| Vitamin A (Beta-Carotene) | 1.67 IU | 0.6 μg |
| Vitamin E (Alpha-Tocopherol) | 1.49 IU | 0.67 mg (670 μg) |
Common Conversions
These reference tables show frequently used vitamin dosages in both micrograms and International Units, helping you compare supplement labels and understand recommended daily amounts.
Vitamin D Conversions
| Micrograms (μg) | International Units (IU) | Common Use |
|---|---|---|
| 10 μg | 400 IU | Minimum daily requirement |
| 25 μg | 1,000 IU | Standard supplement dose |
| 50 μg | 2,000 IU | Higher maintenance dose |
| 75 μg | 3,000 IU | Therapeutic dose |
| 100 μg | 4,000 IU | Upper safe limit (adults) |
| 125 μg | 5,000 IU | High-dose supplementation |
Vitamin A Conversions (Retinol)
| Micrograms (μg) | International Units (IU) | Note |
|---|---|---|
| 300 μg | 1,000 IU | Children’s dose |
| 600 μg | 2,000 IU | Adult female requirement |
| 750 μg | 2,500 IU | Average supplement |
| 900 μg | 3,000 IU | Adult male requirement |
| 1,500 μg | 5,000 IU | Higher dose supplement |
Formulae and Methods
The conversion formulae depend on which substance you’re working with. Here are the key formulae for each major vitamin type.
Vitamin D
From μg to IU: IU = μg × 40
From IU to μg: μg = IU ÷ 40
Example: If you have 25 μg of Vitamin D, multiply by 40 to get 1,000 IU. Conversely, 2,000 IU divided by 40 equals 50 μg.
Vitamin A (Retinol)
From μg to IU: IU = μg × 3.33
From IU to μg: μg = IU ÷ 3.33
Example: 600 μg of retinol equals approximately 2,000 IU (600 × 3.33). Going backwards, 3,000 IU equals roughly 900 μg (3,000 ÷ 3.33).
Vitamin A (Beta-Carotene)
From μg to IU: IU = μg × 1.67
From IU to μg: μg = IU ÷ 1.67
Example: 1,200 μg of beta-carotene equals approximately 2,000 IU. Note that beta-carotene has a different conversion rate than retinol because it must be converted by the body into active vitamin A.
Vitamin E (Alpha-Tocopherol)
From mg to IU: IU = mg × 1.49
From IU to mg: mg = IU × 0.67
Example: 15 mg of alpha-tocopherol equals 22.4 IU (15 × 1.49). Note that Vitamin E is often measured in milligrams rather than micrograms due to higher typical dosages.
Important: Always check the specific form of the vitamin on your supplement label. Different forms (such as retinol versus beta-carotene for Vitamin A, or synthetic versus natural Vitamin E) have different conversion factors.
What Are International Units?
International Units (IU) are a standardised measurement system that quantifies the biological activity or potency of vitamins and certain other substances. Unlike weight-based measurements (such as micrograms or milligrams), IU values reflect how effectively a substance performs its intended biological function in the body.
The World Health Organisation establishes IU standards through scientific testing. Each substance has its own IU definition based on specific biological effects. For example, one IU of Vitamin D represents the activity equivalent to 0.025 μg of cholecalciferol, whilst one IU of Vitamin A (retinol) equals the activity of 0.3 μg of retinol.
Different forms of the same vitamin can have different conversion factors. Vitamin A from retinol and beta-carotene require separate conversions because they have distinct biological activities. Similarly, natural and synthetic forms of Vitamin E have different IU equivalents per unit of weight.
Why Both Units Matter
Supplement labels in the UK and internationally may display vitamin content in either micrograms, milligrams, or International Units—or sometimes both. Being able to convert between these measurements helps you compare products, avoid excessive intake, and follow medical advice accurately.
Healthcare professionals might prescribe vitamins in IU because this measurement directly reflects therapeutic effect. However, many modern labels now prefer metric units (μg or mg) for greater clarity and consistency. Some countries have begun phasing out IU in favour of weight-based measurements, but IU remains widely used, particularly for fat-soluble vitamins.
When comparing supplement products, you may encounter one label showing “1,000 IU Vitamin D” and another displaying “25 μg Vitamin D”. With conversion knowledge, you’ll recognise these are identical doses, helping you make informed purchasing decisions and avoid accidental over-supplementation.