IU to μg Converter

Convert International Units (IU) to micrograms (μg) for vitamins and supplements. Select your substance type and get instant, accurate conversions based on internationally recognised standards.

Conversion Formula & Steps

Converting International Units to micrograms requires a substance-specific conversion factor. Each vitamin has been assigned a unique factor based on its biological activity and molecular weight.

Conversion Factors by Substance

• Vitamin D: Multiply IU by 0.025 (or divide by 40)
• Vitamin A (Retinol): Multiply IU by 0.3
• Vitamin A (Beta-Carotene): Multiply IU by 0.6
• Vitamin E (Natural): Multiply IU by 670
• Vitamin E (Synthetic): Multiply IU by 900

Step-by-Step Conversion

Here’s how to convert 1,000 IU of Vitamin D to micrograms:

• Start with your IU value: 1,000 IU
• Identify the conversion factor: 0.025 for Vitamin D
• Multiply: 1,000 × 0.025 = 25 μg
• Result: 1,000 IU of Vitamin D equals 25 μg

IU to μg Conversion Table

This table shows common vitamin supplement doses converted from International Units to micrograms.

Vitamin D Conversions

Vitamin A Conversions (Retinol)

Vitamin E Conversions

Why Different Conversion Factors?

International Units measure biological activity rather than mass. A vitamin’s potency depends on its molecular structure and how efficiently your body can use it. Natural and synthetic forms of the same vitamin often have different biological activities.

Vitamin D exemplifies this well. Whether you consume D2 (ergocalciferol) or D3 (cholecalciferol), both use the same conversion factor because regulatory bodies consider them bioequivalent. However, Vitamin E natural and synthetic forms differ significantly—natural d-alpha-tocopherol has higher bioavailability than its synthetic counterpart.

Regulatory Standards

The conversion factors used here come from international agreements between scientific organisations and regulatory bodies like the FDA and WHO. These standards help manufacturers label products consistently and enable healthcare providers to prescribe accurate doses regardless of which unit system they use.

Practical Examples

Reading Supplement Labels

You’ll often see vitamin supplements listing doses in IU, particularly for vitamins A, D, and E. A typical Vitamin D supplement sold in the UK might say “1,000 IU (25 μg)” on the label. This dual listing helps you compare products and stay within recommended limits.

Meeting Dietary Guidelines

The NHS recommends 10 μg (400 IU) of Vitamin D daily for most adults during autumn and winter months. If you’re taking a supplement labelled as 400 IU, you’re meeting exactly that recommendation. A 1,000 IU supplement provides 25 μg—two and a half times the minimum.

Medical Prescriptions

Doctors might prescribe higher doses for deficiencies. A common prescription for Vitamin D deficiency is 20,000 IU weekly, which equals 500 μg. Breaking this down, that’s about 2,857 IU (71.4 μg) daily if taken as a daily dose instead.

When to Use Which Unit

Both IU and micrograms remain valid measurement units, though there’s a gradual shift towards metric units in the UK and EU. Older supplement bottles and medical literature often use IU, whilst newer products increasingly list micrograms or milligrams.

Prescription medications tend to use metric units (μg or mg). Over-the-counter supplements vary—some show both units, others only one. Knowing how to convert between them helps you compare products, avoid taking too much, and communicate clearly with healthcare providers.

FAQs

Units Of Vitamin Measurement

Vitamins can be measured in several different units depending on the substance and context.

Related Conversions

If you work with vitamin supplements regularly, you might also need these conversions:

Mass Conversions