Free IU Converter

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

IU is a common label unit for some vitamins (especially Vitamin D). But the IU-to-weight conversion depends on the vitamin and form, which is why you need to select a substance first.

Pick the Substance/form, choose mass → IU, enter your number, and select your mass unit (mcg/mg/g).

No substance selected = no reliable conversion.

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

Yes, for the vitamins/forms supported in this tool. “IU ↔ mg” only works when the vitamin has a defined IU conversion (and for Vitamin E, the natural vs synthetic form matters).

Select Vitamin D (D2/D3) and convert either direction. Vitamin D uses a standard IU factor, so this is one of the most straightforward conversions.

• Natural (d‑alpha‑tocopherol) or
• Synthetic (dl‑alpha‑tocopherol)
  to get the correct result.

mcg RAE = “micrograms of Retinol Activity Equivalents.” It’s the standard way to express Vitamin A activity across retinol and carotenoids.

Because different sources of Vitamin A convert differently. This tool uses standard RAE factors based on the option you choose (food vs supplement carotenoids).

It depends on the vitamin/form. Select the substance (Vitamin D or Vitamin E natural/synthetic), enter 1000 IU, and the tool will show the mg equivalent.