Vitamin D IU to mcg converter

1 mcg of vitamin D = 40 IU. Divide IU by 40 to get mcg; multiply mcg by 40 to get IU. 1,000 IU = 25 mcg = 0.025 mg.

Vitamin D conversion chart

The strengths you'll see most on supplement bottles and prescriptions. Tap a dose for its own page.

The formula

mcg = IU ÷ 40 IU = mcg × 40 mg = mcg ÷ 1,000 mg = IU ÷ 40,000

NIH defines 1 mcg of vitamin D as 40 IU, for both D3 (cholecalciferol) and D2 (ergocalciferol). It doesn't change with the form of the supplement, softgel or drops.

Reading a vitamin D label

US supplement labels now list vitamin D in micrograms, often with IU in brackets, such as "125 mcg (5,000 IU)". The % Daily Value is based on 20 mcg (800 IU). A product that says 625% DV has 125 mcg.

Prescription vitamin D is usually written differently: ergocalciferol 50,000 IU capsules contain 1.25 mg. See 50,000 IU to mg.

How much is in common doses

NIH's recommended amounts are 400 IU (10 mcg) for babies under 12 months, 600 IU (15 mcg) for ages 1 to 70, and 800 IU (20 mcg) from age 71. The upper limit for anyone 9 or older is 4,000 IU (100 mcg) a day. Strengths above that, like 5,000 or 50,000 IU, are normally taken on a clinician's advice. This page converts amounts; it doesn't say how much you should take.

Other vitamins convert differently: see the IU to mg converter for vitamin E, A and insulin.