Pharmaceutical Chemistry
mg/mL to Molarity Calculator
Converts a concentration in mg/mL into molarity, and shows it in M, mM and µM.
Molarity
Enter the concentration in mg/mL and the molecular weight — both greater than zero.
Inputs
Milligrams per millilitre — the same number as g/L.
Also known as molar mass (g/mol or g·mol⁻¹).
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Molarity (M) = Concentration (mg/mL) ÷ Molecular weight (g/mol)
M = (mg/mL) ÷ (g/mol) = (g/L) ÷ (g/mol) = mol/L
A milligram is a thousandth of a gram and a millilitre is a thousandth of a litre, so the thousands cancel: 1 mg/mL = 1 g/L. Dividing grams per litre by grams per mole leaves moles per litre. Multiply by 1000 for mM and by 1,000,000 for µM.
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References
Common questions
Both the numerator and the denominator are scaled by 1000: 1 mg is 0.001 g and 1 mL is 0.001 L. The factors cancel, so the number stays the same and the calculation reduces to dividing by the molecular weight.
Divide by 1000 to get mg/mL first. 500 µg/mL is 0.5 mg/mL. For % w/v, multiply by 10: a 1% w/v solution is 10 mg/mL.
The molecular weight in daltons (Da) or kilodaltons (kDa) — 1 Da equals 1 g/mol, so 66.43 kDa is 66,430 g/mol. Use the mass of the form you have, including tags or glycosylation if they are part of it.
The molarity is rounded to 6 decimal places, so very dilute solutions round to zero. Read the µM figure, or the 4-significant-figure value in the Working section.
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