800 IU of vitamin D to mg and mcg

800 IU of vitamin D = 20 mcg = 0.02 mg. Vitamin D has 40 IU per microgram, so divide IU by 40 to get mcg and by 40,000 to get mg.

How the conversion works

mcg = IU ÷ 40 → 800 ÷ 40 = 20 mcg mg = mcg ÷ 1,000 → 20 ÷ 1,000 = 0.02 mg

The factor comes from the NIH Office of Dietary Supplements: 1 mcg of vitamin D (cholecalciferol, D3, or ergocalciferol, D2) has 40 IU of activity. It works backwards too: 20 mcg × 40 = 800 IU.

Where you'll see 800 IU

800 IU is the RDA for adults over 70 (20 mcg), and the current Daily Value on US supplement labels. Since the FDA's label rules changed (compliance from 2020–2021), supplement labels show vitamin D in mcg, often with IU in brackets: look for 20 mcg (800 IU).

This page converts units; it doesn't recommend a dose. NIH sets the adult upper limit at 4,000 IU (100 mcg) a day. Talk to your clinician about what's right for you.

Convert another amount

Nearby doses

• 400 IU to mg = 10 mcg
• 600 IU to mg = 15 mcg
• 1,000 IU to mg = 25 mcg
• 2,000 IU to mg = 50 mcg

See every common strength in the vitamin D IU to mcg table, or convert vitamin E, A and insulin with the IU to mg converter.