Vitamin D IU to mcg Converter
Vitamin D IU to mcg Converter
Convert vitamin D doses between international units and micrograms, and see how dosing relates to the measured 25-hydroxyvitamin D level.
Vitamin D IU to mcg Converter
IU ⇄ mcgVitamin D dose 1000 IU
Formula
- 40
- IU per microgram, fixed by the international standard for both cholecalciferol (D3) and ergocalciferol (D2)
- 25-hydroxyvitamin D
- the measured storage form, in ng/mL or nmol/L — a different quantity from the dose, not interconvertible with it
Worked example
Vitamin D dose 1000 IU
1000 ÷ 40 = 25.0 mcg
Common doses converted
| IU | mcg |
|---|---|
| 400 | 10 |
| 1000 | 25 |
| 2000 | 50 |
| 10,000 | 250 |
| 50,000 | 1250 |
Dose in IU, measured level in ng/mL — two different numbers
1 mcg of vitamin D equals 40 IU, so a 1000 IU dose is 25 mcg. This conversion applies equally to cholecalciferol (D3) and ergocalciferol (D2), although D3 raises 25-hydroxyvitamin D more effectively per unit dose and is generally the preferred supplement where a choice exists.
Typical maintenance dosing for most adults is 800 to 2000 IU daily. Loading regimens for confirmed deficiency commonly use 50,000 IU weekly for six to eight weeks, or an equivalent cumulative total of around 300,000 IU delivered by another schedule. These loading doses are substantially above daily maintenance and are not meant to be sustained once repletion is achieved.
Toxicity is uncommon below a sustained intake of about 10,000 IU daily, and when it occurs it presents non-specifically — as hypercalcaemia, hypercalciuria and, if prolonged, nephrocalcinosis — rather than with any symptom specific to vitamin D itself. Anyone on high-dose supplementation for an extended period should have serum calcium checked, not only vitamin D.
It is worth being precise about what is being converted here. This calculator converts a dose between IU and mcg. The measured 25-hydroxyvitamin D level — the test used to assess vitamin D status — is reported in ng/mL or nmol/L, a different quantity entirely; multiply ng/mL by 2.496 to obtain nmol/L. Confusing the dose unit with the level unit is a recurring source of error in both prescribing and interpretation.
Frequently asked questions
How many IU are in 1 mcg of vitamin D?
40 IU equal 1 mcg. The conversion is the same for both cholecalciferol (D3) and ergocalciferol (D2).
What is a typical vitamin D maintenance dose?
800 to 2000 IU daily (20 to 50 mcg) for most adults. Loading regimens for deficiency use higher doses, typically 50,000 IU weekly for six to eight weeks.
At what dose does vitamin D become toxic?
Toxicity is uncommon below about 10,000 IU daily sustained. It presents as hypercalcaemia, hypercalciuria and, if prolonged, nephrocalcinosis, so serum calcium should be checked alongside vitamin D in anyone on high-dose therapy.
Is dose in IU the same as the blood level in ng/mL?
No. The dose is measured in IU or mcg; the blood test result — 25-hydroxyvitamin D — is reported in ng/mL or nmol/L and is a separate quantity. Multiply ng/mL by 2.496 to convert it to nmol/L.
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References
- Holick MF, Binkley NC, Bischoff-Ferrari HA, et al. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2011;96(7):1911–1930.
- IOM (Institute of Medicine). Dietary Reference Intakes for Calcium and Vitamin D. National Academies Press; 2011.