Molarity Calculator
Solve for molarity, mass of solute, or volume of solution from any two inputs.
Written by Golam Rabbani, Founder & Lead Engineer
How to use this molarity calculator
- Pick which quantity you want: molarity, mass of solute, or volume of solution.
- Enter the molar mass (g/mol) of the solute.
- Fill in the other two quantities — the tool hides the field you are solving for.
- Press Calculate to see all four related values together (molarity, mass, volume, moles).
- Use Copy to send the result to your clipboard or Reset to start over.
About this molarity calculator
Molarity (M) is the most common measure of solution concentration in chemistry: moles of solute per litre of solution. The defining equation is M = moles ⁄ volume(L) = (mass ⁄ molar mass) ⁄ volume(L). Rearrange it and you can solve for any one of the four quantities — molarity, mass of solute, volume of solution, or molar mass — given the other three.
Worked example: dissolving 5.85 g of sodium chloride (molar mass 58.44 g/mol) in enough water to make exactly 1 L of solution. Moles = 5.85 ⁄ 58.44 = 0.1001 mol. Molarity = 0.1001 ⁄ 1 = 0.100 M — a standard "tenth-molar" saline solution often used in undergraduate labs. Going the other way: how much NaCl do you need for 250 mL of 0.5 M solution? Moles = 0.5 × 0.250 = 0.125 mol, mass = 0.125 × 58.44 = 7.31 g. Always note that "volume of solution" means total volume after dissolving — not the water you start with.
FAQ
- Molarity vs molality — what is the difference?
- Molarity is moles per litre of solution; molality is moles per kilogram of solvent. Molarity changes slightly with temperature (because volume does); molality does not. This tool computes molarity.
- Where do I get the molar mass?
- Add up the atomic weights from the periodic table. Use our atomic mass calculator if you only have the chemical formula — paste in NaCl and you get 58.44 g/mol immediately.
- Can I solve for molar mass too?
- Not directly in this tool — if you have molarity, mass, and volume, compute molar mass = mass ÷ (M × V). The atomic-mass calculator is the better tool when you have the formula.
- Do I need to use volume in liters?
- No — you can enter mL or L; the tool converts. Internally it always works in litres so the M = mol/L definition is exact.
- What if I am preparing a dilution from a stock solution?
- Use M₁V₁ = M₂V₂. Compute the moles you need (M₂V₂), then ask this calculator to tell you the matching mass of dry solute, or compute the dilution by hand.
- Is the molarity calculator free?
- Yes — entirely free, no signup, runs in your browser.