Calcium Unit Converter

In short Calcium is reported in mg/dL in some countries and mmol/L in others, and the two are related by a fixed factor: 1 mg/dL = 0.249513 mmol/L, so to go the other way you divide by 4.00781. 8.5 mg/dL is 2.12 mmol/L; 10.0 mg/dL is 2.50 mmol/L; 10.5 mg/dL is 2.62 mmol/L. The factor is not arbitrary — it comes from the molar mass, because calcium has an atomic mass of 40.078 g/mol, and that is why every analyte has its own factor rather than one shared conversion. Calcium is the analyte where a third unit turns up and causes real confusion: mEq/L. For sodium and potassium, mEq/L and mmol/L are identical because each ion carries one charge — for calcium and magnesium they are not, because those ions carry two, so 2.5 mmol/L is 5.0 mEq/L. Divide by four rather than eight and the answer is exactly double. 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.