Vitamin D (25-OH) Unit Converter

In short Vitamin D (25-OH) is reported in ng/mL in some countries and nmol/L in others, and the two are related by a fixed factor: 1 ng/mL = 2.49602 nmol/L, so to go the other way you divide by 0.400638. 20 ng/mL is 50 nmol/L; 30 ng/mL is 75 nmol/L; 50 ng/mL is 125 nmol/L. The factor is not arbitrary — it comes from the molar mass, because 25-hydroxyvitamin D has a molar mass of 400.64 g/mol, and that is why every analyte has its own factor rather than one shared conversion. The factor is almost exactly 2.5, which makes this one of the few lab conversions that can be done reliably in your head — and one where the two systems produce numbers so different that guidance quoted in one is routinely misread as the other. The widely cited figures of 20 and 30 in ng/mL are 50 and 75 in nmol/L. This converts units. It does not interpret results, does not compare your value against a reference interval, and is not a substitute for the clinician who ordered the test — reference intervals differ between laboratories, methods and populations.