How many IU is 1 mcg of vitamin D?

1 mcg of vitamin D equals 40 IU. So 25 mcg = 1,000 IU, 50 mcg = 2,000 IU, and 100 mcg = 4,000 IU.

Why does my bottle list mcg instead of IU?

Since the 2020 FDA label change, US supplement labels list micrograms (mcg) first, with IU in parentheses. Prescriptions, older bottles, international products, and clinical references still use IU, which is why the two don't always match at a glance.

How much vitamin D per day is too much?

4,000 IU/day (100 mcg) is the adult upper intake level for daily long-term use without supervision. Higher doses are used short-term or under clinician oversight. Actual toxicity needs sustained intake far above that — roughly more than 10,000 IU/day — and shows up only above about 150 ng/mL on a blood test.

Tool

Vitamin D IU ↔ mcg converter

Your bottle says 50 mcg, your doctor said 2,000 IU — same thing? Type either number and this tool converts it (1 mcg = 40 IU) and tells you whether it’s a typical maintenance dose or above the adult daily upper limit.

Amount on your bottle or prescription

Unit

Enter the number on the label and pick its unit. 1 mcg = 40 IU.

Quick reference, not a dosing recommendation. For where these numbers come from — what a healthy level is, the right dose to reach it, and the trial evidence behind it — see the Vitamin D guide.