Vitamin D Calculator — IU to mcg Converter & Daily Dose
Convert vitamin D between IU and mcg, estimate your daily total from supplements and sun, and see where it falls against the NIH RDA of 600–800 IU and the 4,000 IU upper limit.
Age group
IU
Sun exposure
Supplement dose plus estimated sun contribution
- 1
Supplement dose
1,000 IU × 0.025 = 25 mcg1 IU vitamin D = 0.025 mcg - 2
Estimated sun contribution
800 IURough estimate based on selected sun exposure level — highly variable in practice. - 3
Total vitamin D
1,000 + 800 = 1,800
How does this calculator work?
Vitamin D dose in IU × 0.025 = mcg (e.g. 1,000 IU = 25 mcg). The NIH RDA is 600 IU (15 mcg) for adults 19–70, and 800 IU (20 mcg) for 71+. The adult UL is 4,000 IU (100 mcg). Most people in northern latitudes need supplementation in winter to maintain adequate blood levels.
Formula
How this is calculated
Vitamin D exists in two dietary forms: D2 (ergocalciferol, from plants and fortified foods) and D3 (cholecalciferol, from animal sources, fortified foods and supplements). Both are expressed in IU or micrograms — the conversion is exactly 1 IU = 0.025 mcg (equivalently, 1 mcg = 40 IU). The body also synthesises vitamin D3 in the skin on exposure to UVB sunlight, so total daily vitamin D comes from both dietary and cutaneous sources.
The NIH Recommended Dietary Allowance (RDA) for vitamin D is 600 IU (15 mcg) per day for adults aged 19–70, rising to 800 IU (20 mcg) for those over 70, where intestinal absorption and skin synthesis are less efficient. These values assume minimal sun exposure; people with plentiful sun may meet their needs without supplementation.
The Tolerable Upper Intake Level (UL) for adults is 4,000 IU (100 mcg) per day. Chronic intake above the UL can cause hypercalcaemia — elevated blood calcium — leading to nausea, weakness, kidney damage and calcification of soft tissues. The sun-exposure estimates in this calculator are approximate guidelines only: actual cutaneous synthesis depends on skin tone, latitude, season, time of day, cloud cover and sunscreen use. Serum 25-hydroxyvitamin D [25(OH)D] measured by a blood test is the only reliable indicator of actual status.
Frequently asked questions
The NIH RDA is 600 IU for adults 19–70 and 800 IU for those over 70. Many doctors recommend 1,000–2,000 IU/day for people at risk of deficiency (limited sun exposure, darker skin, obesity, older age), staying well below the 4,000 IU UL unless advised otherwise.
The Endocrine Society and most guidelines define vitamin D sufficiency as a serum 25(OH)D level ≥ 20 ng/mL (50 nmol/L), with an optimal range often cited as 40–60 ng/mL for bone health. However, blood levels respond very differently to the same supplement dose across individuals.
Very few foods naturally contain significant vitamin D — oily fish (salmon, mackerel) and egg yolks are the main sources, plus fortified foods (milk, orange juice, cereals in some countries). Most people in low-sunlight regions rely on supplementation to meet the RDA.
Also known as
TG we-Calculate Editorial Team. (2026). Vitamin D Calculator — IU to mcg Converter & Daily Dose [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/vitamin-d-calculator
TG we-Calculate Editorial Team. "Vitamin D Calculator — IU to mcg Converter & Daily Dose." TG we-Calculate. 2026. https://we-calculate.com/calculator/vitamin-d-calculator.
TG we-Calculate Editorial Team, "Vitamin D Calculator — IU to mcg Converter & Daily Dose," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/vitamin-d-calculator
@misc{wecalculate_vitamin_d_calculator, title = {Vitamin D Calculator — IU to mcg Converter & Daily Dose}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/vitamin-d-calculator}}, year = {2026}, note = {TG we-Calculate} }
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