Vitamin D Calculator: Convert nmol/l to ng/ml and IU to µg

With the Vitamin D Calculator you can convert your lab result from ng/ml to nmol/l (and back), and vitamin D amounts from IU to µg, per day, week or month. Below it you will find the table of normal values according to the DGE (German Nutrition Society) and the Institute of Medicine, the EFSA upper limit, and the formula that studies use to calculate the loading dose.

By Simon Gütter · Values according to the DGE, EFSA and IOM · Last updated: November 2026 · free, no sign-up, nothing stored

Vitamin D level chart: what is a normal vitamin D level?

A vitamin D level of 50 nmol/l (20 ng/ml) or above is considered sufficient, and a level below 30 nmol/l (12 ng/ml) is considered deficient. What is measured is 25-OH vitamin D in the blood, the storage form of the vitamin. Laboratories report the value in nmol/l or ng/ml, which is why both units are shown here.

In Germany, more than half of adults fall below this: in the RKI (Robert Koch Institute) study DEGS1, 61.6 per cent had less than 50 nmol/l, and in winter one in four had less than 30 nmol/l [5].

Vitamin D dose calculator: how studies calculate the loading dose

How much vitamin D is needed for a deficiency is decided by your doctor’s surgery. In the medical literature there is a frequently cited formula from a clinical study. We explain it here so that you can understand how such amounts come about. The calculator above deliberately does not calculate with your personal data.

Loading dose using the van Groningen formula

In a study of 208 adults with a deficiency, the level rose by 0.025 nmol/l per IU per kilogram of body weight. From this, the researchers derived the formula: Dose (IU) = 40 × (75 − level in nmol/l) × body weight in kg [1]. Example: for 80 kg and 15 ng/ml (37.5 nmol/l), the formula gives 40 × 37.5 × 80 = 120,000 IU, which spread over 8 weeks is around 2,140 IU per day.

In the study, only people with a deficiency below 50 nmol/l were given a loading dose. The table shows what the formula gives for different starting values and weights.

A level of 20 ng/ml (50 nmol/l) is already considered sufficient. The last row only shows what the formula would give up to 75 nmol/l. The figures are worked examples from the study, not a recommendation for you.

Reference value afterwards: why weight and BMI matter

For the period afterwards, the DGE reference value of 20 µg (800 IU) per day applies when the skin produces hardly any vitamin D [2]. With more body fat, the level rises less with the same dose. In an analysis of 17,614 adults, people who were overweight had levels that were on average 8.0 nmol/l lower, and people with obesity 19.8 nmol/l lower. To reach a level of 100 nmol/l, an average of 2,080 IU (normal weight), 3,065 IU (overweight) and 5,473 IU per day (obesity) was needed. From this, the researchers derive 1.5 times the dose for overweight and 2 to 3 times for obesity [3]. It was an observational study from a prevention programme. The EFSA upper limit of 4,000 IU per day still applies.

Why 4,000 IU is the limit

In 2023, EFSA set a safe upper limit for adults of 100 µg (4,000 IU) per day. The basis was that in two studies, a persistently raised excretion of calcium in the urine occurred from 250 µg daily. Applying a safety factor of 2.5, EFSA derived the limit of 100 µg from this [4]. Many other calculators aim for 50 to 100 ng/ml. There is no proven additional benefit for such levels, and the Institute of Medicine regards levels above 125 nmol/l (50 ng/ml) as a possible cause for concern [6].

How much vitamin D a day? Dosage for adults

For adults, the DGE gives an estimated value of 800 IU (20 µg) of vitamin D per day where there is no production in the skin. A typical diet supplies only 80 to 160 IU of this [2]. From spring to autumn, the skin produces a large part itself in sunshine. In winter, this is usually not enough in Germany.

• Dietary supplements: The German Federal Institute for Risk Assessment (Bundesinstitut für Risikobewertung, BfR) recommends a maximum of 20 µg (800 IU) per daily dose for these [7]. Higher-dose products are medicines or are intended to be taken under medical supervision.
• Daily rather than a single large dose: Very large single doses perform poorly in studies. In a study of 2,256 older women, a yearly single dose of 500,000 IU, given each autumn or winter over 3 to 5 years, led to more falls and fractures: 171 fractures instead of 135 in the placebo group [8].
• With food: Vitamin D is fat-soluble. In one study, the level rose markedly when participants took their supplement with their largest meal [9]. In a randomised study, vitamin D was absorbed somewhat better in the short term with a low-fat meal than on an empty stomach or with a lot of fat, but the level after 30 and 90 days did not differ [10].

Vitamin D overdose: when does it become dangerous?

Vitamin D becomes dangerous when significantly more than 4,000 IU per day is taken over a long period. Too much calcium then builds up in the body, known as hypercalcaemia. It can weaken bones and damage the kidneys and heart [11]. An overdose does not arise from diet alone or from sunshine; it almost always comes from high-dose supplements.

According to EFSA, amounts above 4,000 IU per day should be taken under medical supervision, with monitoring of vitamin D and calcium levels [4]. With kidney disease, kidney stones, sarcoidosis or raised calcium, vitamin D is always a matter for your doctor’s surgery.

Frequently asked questions about the vitamin D calculator and taking vitamin D

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Note on the data and on use

The vitamin D calculator is a pure unit converter (ng/ml and nmol/l, IU and µg, day, week and month). It does not process any personal health data, does not evaluate lab values and gives no dosage recommendation. It is not a medical device. The texts and tables on this page summarise published guidelines and studies (DGE, EFSA 2023, Institute of Medicine 2011, van Groningen et al. 2010, Ekwaru et al. 2014). They serve as general information and are no substitute for a medical examination, diagnosis or advice. Whether and how much vitamin D you take is something to discuss with your doctor’s surgery. Your entries stay in your browser and are neither stored nor transmitted. Sources last checked: November 2026.

Sources

1. van Groningen L, Opdenoordt S, van Sorge A et al.: Cholecalciferol loading dose guideline for vitamin D-deficient adults. Eur J Endocrinol 2010. PubMed 20139241. DOI: 10.1530/EJE-09-0932.
2. Deutsche Gesellschaft für Ernährung (German Nutrition Society): Reference values for vitamin D. dge.de.
3. Ekwaru JP, Zwicker JD, Holick MF et al.: The importance of body weight for the dose response relationship of oral vitamin D supplementation and serum 25-hydroxyvitamin D in healthy volunteers. PLoS One 2014. PubMed 25372709. DOI: 10.1371/journal.pone.0111265.
4. EFSA Panel on Nutrition, Novel Foods and Food Allergens: Scientific opinion on the tolerable upper intake level for vitamin D. EFSA J 2023. PubMed 37560437. DOI: 10.2903/j.efsa.2023.8145.
5. Rabenberg M, Scheidt-Nave C, Busch MA et al.: Vitamin D status among adults in Germany – results from the German Health Interview and Examination Survey for Adults (DEGS1). BMC Public Health 2015. PubMed 26162848. DOI: 10.1186/s12889-015-2016-7.
6. Ross AC, Manson JE, Abrams SA 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. DOI: 10.1210/jc.2010-2704.
7. Bundesinstitut für Risikobewertung (German Federal Institute for Risk Assessment): Proposed maximum levels for vitamin D in foods, including food supplements. bfr.bund.de.
8. Sanders KM, Stuart AL, Williamson EJ et al.: Annual high-dose oral vitamin D and falls and fractures in older women: a randomized controlled trial. JAMA 2010. PubMed 20460620. DOI: 10.1001/jama.2010.594.
9. Mulligan GB, Licata A: Taking vitamin D with the largest meal improves absorption and results in higher serum levels of 25-hydroxyvitamin D. J Bone Miner Res 2010. PubMed 20200983. DOI: 10.1002/jbmr.67.
10. Dawson-Hughes B, Harris SS, Lichtenstein AH et al.: Meal conditions affect the absorption of supplemental vitamin D3 but not the plasma 25-hydroxyvitamin D response to supplementation. J Bone Miner Res 2013. PubMed 23427007. DOI: 10.1002/jbmr.1896.
11. NHS: Vitamin D. nhs.uk.
12. Demay MB, Pittas AG, Bikle DD et al.: Vitamin D for the Prevention of Disease: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab 2024. PubMed 38828931. DOI: 10.1210/clinem/dgae290.