Vitamin D IU to mcg: Conversion Table (400 IU = 10 mcg)
For vitamin D3, 40 IU equals 1 mcg: 400 IU = 10 mcg, 1,000 IU = 25 mcg, 2,000 IU = 50 mcg and 5,000 IU = 125 mcg. To go from IU to mcg, divide by 40. To go from mcg to IU, multiply by 40.
By Erin Rose Updated October 20, 2026 How we score
Vitamin D IU to mcg table
| IU | mcg | What it is |
|---|---|---|
| 400 IU | 10 mcg | Babies’ daily need; below the adult RDA of 600 IU |
| 600 IU | 15 mcg | Adult RDA, ages 1 to 70 |
| 800 IU | 20 mcg | Adult RDA, 71 and older |
| 1,000 IU | 25 mcg | A common supplement; covers the RDA |
| 2,000 IU | 50 mcg | A common supplement; under the 4,000 IU upper limit |
| 4,000 IU | 100 mcg | The adult upper limit |
| 5,000 IU | 125 mcg | Above the upper limit; take on a doctor’s advice |
| 10,000 IU | 250 mcg | Above the upper limit; doctor-directed doses only |
Most adults need 600 IU (15 mcg) a day up to age 70 and 800 IU (20 mcg) after that. The upper limit for adults is 4,000 IU (100 mcg) a day from all sources (Ross 2011).
Which vitamin D should you buy?
Most adults: 2,000 IU (50 mcg)
50 mcg (2,000 IU) is one NatureWise D3 softgel, our pick. It is on NSF/ANSI 173 and under the 4,000 IU (100 mcg) limit.
NatureWise Vitamin D3 2000 IU in Olive Oil
$0.04 a day · 2,000 IU (50 mcg) · NSF/ANSI 173
Want a lower dose: 1,000 IU (25 mcg)
NatureWise D3 1000 IU is one small softgel of 1,000 IU, enough for most adults who get some sun. It is on NSF/ANSI 173, a list that checks the bottle holds what the label says.
NatureWise Vitamin D3 1000 IU in Olive Oil
$0.03 a day · 1,000 IU (25 mcg)
Not sure which strength?
See 1,000 vs 5,000 IU and the best vitamin D for your needs.
Why labels show two units
US labels must give vitamin D in mcg, the weight of the vitamin (NIH). Many brands still print IU too, the older unit that measures how strong a dose is. For vitamin D3 the two always convert at 40 IU to 1 mcg, so a bottle that says “50 mcg (2,000 IU)” means the same dose twice.
Questions people ask
How many IU is 125 mcg of vitamin D?
5,000 IU. Multiply mcg by 40.
Does 40 IU per mcg work for other vitamins?
No. The factor of 40 is for vitamin D only. Vitamins A and E use different factors.
Sources
- NIH Office of Dietary Supplements, “Vitamin D: Fact Sheet for Health Professionals” (1 mcg = 40 IU; RDA and upper limit). ods.od.nih.gov
- Ross AC, et al. “The 2011 report on dietary reference intakes for calcium and vitamin D from the Institute of Medicine: what clinicians need to know.” J Clin Endocrinol Metab. 2011. PubMed 21118827