IU to mcg/mg Converter (and mcg/mg to IU)

Q: What does IU mean?

IU means International Unit . It measures potency (biological activity) , not weight, so IU isn’t automatically the same as mcg, mg, or g .

Q: Why do I need to select a substance/form first?

IU-to-mass conversions depend on the vitamin and form. For example, Vitamin E differs by natural vs synthetic , and Vitamin A is handled as mcg RAE on modern labels. No substance selected = no reliable conversion.

Q: How do I convert mass → IU using this tool?

Select the Substance/form , choose mass → IU , enter your value, and choose your mass unit (mcg/mg/g) . The calculator will apply the correct factor for the selected form.

Q: How do I convert IU → mass using this tool?

Select the Substance/form , choose IU → mass, enter your IU value, then choose whether you want the result in mcg, mg, or g.

Q: Vitamin D: is IU conversion straightforward?

Yes. Vitamin D is one of the most consistent conversions: 1 IU = 0.025 mcg 1 mcg = 40 IU (Works for D2 and D3 .)

Q: What is mcg RAE (Vitamin A)?

mcg RAE means micrograms of Retinol Activity Equivalents. It’s the modern way to express Vitamin A activity across different sources (retinol and carotenoids) with different bioavailability.

Q: How do I see Vitamin A in IU?

Vitamin A is shown as mcg RAE under the FDA (US) and CFIA (Canada) label standards. If you need IU, switch Label standard → Legacy IU reference to show IU conversions for Vitamin A.

Q: Why does Vitamin E have two different conversions (natural vs synthetic)?

Vitamin E conversions differ by form: natural (d‑alpha‑tocopherol) vs synthetic (dl‑alpha‑tocopherol). Always match the factor to the form on your label. This tool supports both.

Convert IU to mcg, IU to mg, and mcg/mg to IU for common vitamin labelling and formulation workflows. Because International Units (IU) measure biological activity (not weight), conversions depend on the vitamin and form. Select the correct Substance/form to get an accurate result.

Best for: Vitamin D (D2/D3), Vitamin E (natural vs synthetic), and Vitamin A using mcg RAE (including beta‑carotene food vs supplement sources).

Label standard

Substance / form

Convert

Mass unit

Value

Result

Enter a value to see the result.

How to use this IU converter?

Choose a Label standard: FDA (US), CFIA (Canada), or Legacy IU reference.
Select the Substance/form (for example: Vitamin D, Vitamin E natural, Vitamin A as mcg RAE, or a Vitamin A carotenoid source).
Pick the conversion direction (for example: IU → mass or mass → IU).
Enter your value and choose your mass unit (mcg, mg, or g).
Copy the result.

What does “Label standard” mean?

FDA (US) / CFIA (Canada) reflect modern label units where applicable:

Vitamin A is typically shown as mcg RAE (Retinol Activity Equivalents)
Vitamin E is typically shown as mg alpha‑tocopherol
Vitamin D is commonly shown as mcg, often with IU referenced.

Legacy IU reference is included for older IU-based references (especially for Vitamin A). If you need IU for Vitamin A, switch to the Legacy IU reference.

Supported vitamins and forms

Vitamin D (D2/D3)

Vitamin E (natural, d‑alpha‑tocopherol)

Vitamin E (synthetic, dl‑alpha‑tocopherol)

Vitamin A (mcg RAE)

Vitamin A (retinol, mcg retinol)

Vitamin A (beta‑carotene, supplements, mcg)

Vitamin A (beta‑carotene, food, mcg)

Vitamin A (alpha‑carotene, food, mcg)

Vitamin A (beta‑cryptoxanthin, food, mcg)

IU is potency, not weight (why the form matters)

An International Unit (IU) measures potency (biological activity). That’s why 1 IU does not equal a fixed mass across different vitamins, and sometimes even differs by form.

Vitamin D: standardized conversion (straightforward)
Vitamin E: conversion differs for natural vs synthetic forms
Vitamin A: modern labelling uses mcg RAE, and conversions depend on whether Vitamin A comes from retinol or carotenoids

Quick Reference

Vitamin D (D2/D3): IU ↔ mcg

1 IU = 0.025 mcg
1 mcg = 40 IU

Vitamin E (alpha‑tocopherol): IU ↔ mg (legacy reference)

Natural (d‑alpha‑tocopherol): 1 IU = 0.67 mg
Synthetic (dl‑alpha‑tocopherol): 1 IU = 0.45 mg

Vitamin A: mcg RAE (modern) + legacy IU reference

Modern labels typically use mcg RAE for Vitamin A. In Legacy IU reference mode, this tool can show an approximate IU bridge:

1 mcg RAE ≈ 3.33 IU (legacy reference)

Vitamin A (RAE) mcg conversions

Vitamin A source	Conversion to mcg RAE
Retinol	1 mcg = 1 mcg RAE
Beta‑carotene (supplements)	2 mcg = 1 mcg RAE
Beta‑carotene (food)	12 mcg = 1 mcg RAE
Alpha‑carotene (food)	24 mcg = 1 mcg RAE
Beta‑cryptoxanthin (food)	24 mcg = 1 mcg RAE

Tip: If you’re converting Vitamin A and need IU, switch Label standard → Legacy IU reference.

Vitamin D conversions

Vitamin D IU → mcg

IU	mcg
400 IU	10 mcg
800 IU	20 mcg
1,000 IU	25 mcg
2,000 IU	50 mcg
5,000 IU	125 mcg
10,000 IU	250 mcg

Using IU conversions for Supplement Facts and nutrition labelling

If you’re creating or updating a Supplement Facts label, you may need to convert older IU-based amounts into mcg or mg, depending on the nutrient and form (especially for Vitamin A and Vitamin E).

MenuSano helps food and supplement businesses generate compliant labels and nutrition analysis outputs:

FAQ

What does IU mean?

IU means International Unit. It measures potency (biological activity), not weight, so IU isn’t automatically the same as mcg, mg, or g.

Why do I need to select a substance/form first?

IU-to-mass conversions depend on the vitamin and form. For example, Vitamin E differs by natural vs synthetic, and Vitamin A is handled as mcg RAE on modern labels.

No substance selected = no reliable conversion.

How do I convert mass → IU using this tool?

Select the Substance/form, choose mass → IU, enter your value, and choose your mass unit (mcg/mg/g). The calculator will apply the correct factor for the selected form.

How do I convert IU → mass using this tool?

Select the Substance/form, choose IU → mass, enter your IU value, then choose whether you want the result in mcg, mg, or g.

Can I convert IU to mg for any vitamin?

Only when that vitamin/form has a defined IU conversion factor. IU is not a universal weight unit, so “IU → mg” only works for substances with an established standard.

Vitamin D: is IU conversion straightforward?

Yes. Vitamin D is one of the most consistent conversions:

1 IU = 0.025 mcg
1 mcg = 40 IU
(Works for D2 and D3.)

What is mcg RAE (Vitamin A)?

mcg RAE means micrograms of Retinol Activity Equivalents. It’s the modern way to express Vitamin A activity across different sources (retinol and carotenoids) with different bioavailability.

Why does Vitamin A conversion depend on the source (retinol vs carotenoids)?

Because different Vitamin A sources convert differently to activity (RAE). For example, beta‑carotene from food is not equivalent to retinol mcg-for-mcg. This tool uses standard RAE factors based on the option you choose (food vs supplement carotenoids).

How do I see Vitamin A in IU?

Vitamin A is shown as mcg RAE under the FDA (US) and CFIA (Canada) label standards. If you need IU, switch Label standard → Legacy IU reference to show IU conversions for Vitamin A.

Why does Vitamin E have two different conversions (natural vs synthetic)?

Vitamin E conversions differ by form: natural (d‑alpha‑tocopherol) vs synthetic (dl‑alpha‑tocopherol). Always match the factor to the form on your label. This tool supports both.

What is 1,000 IU in mg?

It depends on the vitamin/form. Select the Substance/form, enter 1,000 IU, and the tool will show the correct mg (or mcg) equivalent for that form.

Does this tool replace professional advice?

No. This tool is for conversions and labeling/formulation workflows. For medical dosing decisions, consult a qualified professional.

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