Microgram ↔ IU Conversion

Select a nutrient to convert between weight-based dosing (micrograms) and biological activity (International Units). Reference data follows NIH dietary supplement guidance.

Nutrient

Used for bone health and immune modulation. 1 mcg = 40 IU.

Conversion direction

Amount (mcg)

Conversion Result

Vitamin D₃ (cholecalciferol)

25 mcg = 1,000 IU

Conversion factor: 1 mcg = 40 IU.

Source: US NIH Office of Dietary Supplements

How to Use This Calculator

1

Select the vitamin form

Different nutrients use unique IU definitions. Choose the correct vitamin form (e.g., vitamin D₃).

2

Enter the amount and units

Convert supplement labels (often in IU) or prescription orders (commonly mcg or mg).

3

Apply clinically

Use the converted value to verify dosing, compare products, or counsel patients on intake.

Formula

IU = mcg × IU per microgram

mcg = IU ÷ IU per microgram

Conversion factors differ by nutrient and sometimes by chemical form (natural vs synthetic).