Molarity Calculator
Find the molarity (mol/L) of a solution from the mass of solute, its molar mass and the solution volume, for preparing reagents, buffers and standards.
Last updated: October 2026
Molarity
0.5 M
Formula below · 3 sources (NIST, goldbook.iupac.org, chem.libretexts.org) · Updated Oct 2026
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About this calculator
Molarity is moles of solute per liter of solution:
M = (mass ÷ molar mass) ÷ volume
Dividing the mass in grams by the molar mass in g/mol gives moles; dividing by the volume of the finished solution in liters gives mol/L, written M. Rearranged, the mass to weigh for a target molarity is mass = M × volume × molar mass.
The volume is the total solution volume, not the volume of water. Dissolve the solute in less solvent, then fill to the mark in a volumetric flask. Because liquids expand when warmed, a molarity strictly applies at the temperature where the volume was made up, usually 20 or 25 °C. For a temperature-independent measure, use molality (moles per kilogram of solvent).
| Compound | Formula | Molar mass (g/mol) |
|---|---|---|
| Sodium chloride | NaCl | 58.44 |
| Potassium chloride | KCl | 74.55 |
| Sodium hydroxide | NaOH | 40 |
| Glucose | C6H12O6 | 180.16 |
| Copper(II) sulfate pentahydrate | CuSO4·5H2O | 249.68 |
| Sucrose | C12H22O11 | 342.3 |
How to use
Enter the grams of solute, its molar mass and the final solution volume in liters (500 mL = 0.5 L). The default dissolves 29.22 g of sodium chloride (58.44 g/mol) to 1 L: 29.22 ÷ 58.44 = 0.5 mol, and 0.5 mol ÷ 1 L = 0.5 M. Made up to 0.5 L instead, the same salt gives 1 M. To make 250 mL of 0.1 M glucose (180.16 g/mol), weigh 0.1 × 0.25 × 180.16 = 4.5 g; entering 4.504 g, 180.16 and 0.25 here confirms 0.1 M.
Frequently asked questions
What is the difference between molarity and molality?
Molarity is moles per liter of solution; molality is moles per kilogram of solvent. Molality does not change with temperature, so it is used for boiling-point and freezing-point calculations. For dilute water solutions near room temperature the two are close.
How many grams do I need for a given molarity?
Multiply molarity × volume in liters × molar mass. For 2 L of 0.15 M potassium chloride (74.55 g/mol): 0.15 × 2 × 74.55 = 22.37 g.
How do I convert percent (w/v) to molarity?
% w/v is grams per 100 mL, so multiply by 10 to get g/L and divide by the molar mass. A 0.9% w/v saline solution is 9 g/L ÷ 58.44 g/mol = 0.154 M.
Where do I find the molar mass?
Add up the standard atomic weights of the atoms in the formula. Use the hydrate formula if your reagent bottle says it is a hydrate: CuSO4·5H2O is 249.68 g/mol, anhydrous CuSO4 159.60 g/mol.
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