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Vitamin D converter: IU to mcg and back

Written by the Full Measure editorial team, which sells supplements. Approved for publication by the Full Measure owners. Updated .

Drafted with AI assistance from the sources listed below. How we write these

Quick answer

For vitamin D, 1 mcg equals 40 IU. Divide IU by 40 to get micrograms, or multiply micrograms by 40 to get IU. So 600 IU is 15 mcg, 2,000 IU is 50 mcg and 4,000 IU is 100 mcg. Enter either number in the converter and the other fills in.1

Convert IU and micrograms

For vitamin D, 1 mcg is 40 IU. Other vitamins convert differently.

Key facts

  • Adults aged 19 to 70 need 15 mcg (600 IU) of vitamin D a day, and adults aged 71 and older need 20 mcg (800 IU).1,2
  • Labels must list vitamin D in mcg and may also show IU. The Daily Value on labels is 20 mcg (800 IU).1
  • The adult upper limit is 100 mcg (4,000 IU) a day from all sources.1,2
  • VITAL and DO-HEALTH, two of the largest trials of vitamin D, both gave 50 mcg (2,000 IU) of vitamin D3 a day.3,4

How the converter works

Type a number in the IU box and the micrograms box fills in, dividing by 40. Type in the micrograms box and the IU box fills in, multiplying by 40. Answers are rounded to two decimal places, and nothing you type leaves your browser.1

For vitamin D, 1 mcg equals 40 IU. So 10 mcg is 400 IU, 15 mcg is 600 IU, 50 mcg is 2,000 IU and 100 mcg is 4,000 IU.1

Common vitamin D amounts

Vitamin D amounts in IU and micrograms1,2,3,4
IUMicrograms (mcg)Where the amount comes from
400 IU10 mcgRecommended for babies up to 12 months
600 IU15 mcgRecommended for adults aged 19 to 70
800 IU20 mcgRecommended for adults 71 and older, and the Daily Value on labels
1,000 IU25 mcgConverted: 1,000 divided by 40
2,000 IU50 mcgThe amount VITAL and DO-HEALTH gave each day
4,000 IU100 mcgThe adult upper limit

The 1,000 IU row is simple arithmetic. The other rows are amounts that NIH or the trials give.1

Which number to follow

Follow the unit printed on your product, and convert it here when another source gives the other unit. These are the amounts NIH and the largest trials use.

Food labels must list vitamin D in mcg and may also show the IU amount. The Daily Value used on labels is 20 mcg (800 IU) for adults and children aged 4 and older.1

Adults aged 19 to 70 need 15 mcg (600 IU) of vitamin D a day, the same amount during pregnancy and breastfeeding.1,2

Adults aged 71 and older need 20 mcg (800 IU) a day.1,2

VITAL and DO-HEALTH, two of the largest trials of vitamin D, both gave 50 mcg (2,000 IU) of vitamin D3 a day.3,4

Other vitamins convert differently

The rule of 40 IU to 1 mcg is for vitamin D only. For vitamin E, as one example, 1,000 mg is 1,500 IU of the natural form but 1,100 IU of the synthetic form, so the same weight gives a different number of IU.5

Upper limit and who should ask first

The upper limit for adults and children aged 9 and over is 100 mcg (4,000 IU) a day from all sources, including during pregnancy and breastfeeding. It is 25 mcg (1,000 IU) for babies up to 6 months, 38 mcg (1,500 IU) from 7 to 12 months, 63 mcg (2,500 IU) at ages 1 to 3 and 75 mcg (3,000 IU) at ages 4 to 8. Signs of toxicity are unlikely below 250 mcg (10,000 IU) a day, but NIH notes that even intakes below the upper limit might cause harm over time.1,2

  • You are pregnant or nursing, or you want to give vitamin D to a baby or child. Amounts differ by age, so ask first.
  • You have high blood calcium, kidney disease, kidney stones or an overactive parathyroid gland.
  • You take a thiazide water pill, a statin, steroid tablets, orlistat or a bile acid sequestrant such as cholestyramine.
  • You already take a multivitamin, calcium with vitamin D, cod liver oil or prescription vitamin D. Add up every source, and check combinations of our own products with the upper limit checker.

Questions people ask

How many IU is 50 mcg of vitamin D?

It is 2,000 IU. Multiply micrograms by 40, and 50 times 40 is 2,000.1

How many mcg is 1,000 IU of vitamin D?

It is 25 mcg. Divide IU by 40, and 1,000 divided by 40 is 25.1

Is IU the same as mcg?

No. They are different units. For vitamin D, 1 mcg equals 40 IU, but other vitamins use other conversions, and some even depend on the form of the vitamin.1,5

Is 4,000 IU a day too much?

4,000 IU, which is 100 mcg, is the adult upper limit from all sources, food included. NIH notes that even intakes below the upper limit might cause harm over time, so ask your doctor before going near it.1,2

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Sources

  1. National Institutes of Health, Office of Dietary Supplements. Vitamin D: Fact Sheet for Health Professionals. Updated June 27, 2025. Opened 2026-10-07.
  2. Office of Dietary Supplements, National Institutes of Health. Vitamin D: Fact Sheet for Consumers. Updated November 8, 2022. Opened 2026-10-07.
  3. Manson JE, et al. Vitamin D Supplements and Prevention of Cancer and Cardiovascular Disease. N Engl J Med. 2019;380(1):33-44. Opened 2026-10-01.
  4. Bischoff-Ferrari HA, et al. Effect of Vitamin D Supplementation, Omega-3 Fatty Acid Supplementation, or a Strength-Training Exercise Program on Clinical Outcomes in Older Adults: The DO-HEALTH Randomized Clinical Trial. JAMA. 2020;324(18):1855-1868. Opened 2026-10-01.
  5. National Institutes of Health, Office of Dietary Supplements. Vitamin E: Fact Sheet for Health Professionals. Updated March 26, 2021. Opened 2026-10-07.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.