How do you convert calcium from mg/dL to mmol/L?

Divide by the molar mass. For calcium (40.078 g/mol), 1 mg/dL = 0.249513 mmol/L.

Why isn't there one factor for mg/dL to mmol/L?

Because mg measures mass and mmol measures amount of substance, the factor depends on the molar mass of what is being measured. Every analyte has its own.

Calculators › Calcium

Calcium: mg/dL to mmol/L

1 mg/dL = 0.249513 mmol/L

Reference only. These conversions are arithmetic, not medical advice. Reference ranges differ between laboratories, and results should be interpreted by a clinician alongside the lab's own reported units and ranges.

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Conversion table

mg/dL	mmol/L
8 mg/dL	1.9961 mmol/L
8.5 mg/dL	2.1209 mmol/L
9 mg/dL	2.2456 mmol/L
9.5 mg/dL	2.3704 mmol/L
10 mg/dL	2.4951 mmol/L
10.5 mg/dL	2.6199 mmol/L
11 mg/dL	2.7446 mmol/L
12 mg/dL	2.9942 mmol/L

Going the other way, 1 mmol/L = 4.0078 mg/dL.

Why this conversion needs the substance

mg/dL measures mass; mmol/L measures amount of substance. Converting between them needs the molar mass of the thing being measured — for calcium that is 40.078 g/mol. That is why a generic converter can't do it, and why every analyte has a different factor.

Jotal works this out from molar mass rather than a stored factor, so write calcium 10 mg/dL in mmol/L and it answers 2.4951 mmol/L. Leave the substance out and it deliberately returns nothing rather than guessing.

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