Guides
How to Calculate Concentration (Molarity): n=m/M and c=n/V
Molarity c (mol/L) = amount of solute n ÷ solution volume V. First convert mass to moles with n = m/M, then divide by the volume in litres.
Formulas
n = m / M (moles = mass ÷ molar mass), c = n / V (concentration = moles ÷ volume). Use litres (L) for V.
Steps
- Find molar mass M Compute the solute's molar mass (g/mol) from its formula.
- Find moles n n = m / M.
- Find concentration c Convert volume to litres, then c = n / V.
- To prepare a solution Mass needed m = c × V × M.
Worked example
Dissolve 4 g NaOH (M=40) to make 500 mL of solution — what is the concentration?
n = 4 / 40 = 0.1 mol → c = 0.1 / 0.5 = 0.2 mol/L
Reverse: to make 250 mL of 0.1 mol/L NaCl, you need m = 0.1 × 0.25 × 58.44 ≈ 1.46 g.
Use the tool
Enter mass, molar mass and volume in the concentration calculator; for molar mass see the molar mass guide.