Pharmaceutical Chemistry
Mass Molarity Calculator
Works out the molarity of a solution from the mass of solute you weighed, its molar mass and the final volume.
Molarity
Enter the mass, molar mass and volume — all greater than zero.
Inputs
The mass you weighed on the balance, in grams.
Also called molecular weight. NaCl is 58.44 g/mol.
Final volume in litres — 100 mL is 0.1 L.
Try an example
Molarity (M) = (Mass ÷ Molar mass) ÷ Volume
M = (g ÷ g·mol⁻¹) ÷ L = mol·L⁻¹
Mass is the solute in grams, molar mass is in g/mol and volume is the final volume of solution in litres. Dividing mass by molar mass gives the amount in moles; dividing that by the volume gives moles per litre.
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References
Common questions
Divide by 1000 first. 250 mL is 0.25 L and 50 mL is 0.05 L. Entering 250 instead of 0.25 gives an answer 1000 times too small.
No. Molarity is moles per litre of solution; molality is moles per kilogram of solvent. They are close for dilute aqueous solutions but differ for concentrated ones, and molarity changes slightly with temperature because volume does.
The result is rounded to 4 decimal places, so anything below 0.00005 M rounds to zero. The Working section also gives the value to 4 significant figures, which shows very dilute concentrations properly.
The molar mass of exactly what you weighed. Copper sulfate pentahydrate (CuSO₄·5H₂O) is 249.68 g/mol, while anhydrous CuSO₄ is 159.61 g/mol — using the wrong one gives a concentration about 1.6 times off.
Multiply by 1000. 0.0111 M is 11.1 mM, and 1 M is 1000 mM.
Prepared by the PharmaWallah student team. Verify results with your textbook or instructor. Report an error · Editorial policy