Use our Molarity Calculator to quickly compute solution concentration in mol/L (M). Enter either moles of solute or mass plus molar mass, choose your solution volume, and get an accurate result with adjustable decimal precision.
What is molarity?
Molarity, symbolized as M, is the number of moles of solute per liter of solution. It is one of the most common ways chemists express concentration because it directly relates the amount of solute to the total volume of the final solution. The core formula is simple: M = moles of solute / liters of solution. Since volume changes with temperature, molarity is temperature dependent; however, it remains the go-to unit for titrations, reaction stoichiometry, and many laboratory preparations.
How to use the Molarity Calculator
- Select an input method. Choose “I know moles of solute” if you already have the amount in moles, or choose “I know mass of solute and molar mass” to calculate moles from grams.
- Enter your quantity. If you chose moles, fill in the moles field. If you chose mass, enter both the mass of solute (in grams) and its molar mass (g/mol).
- Enter the total solution volume and pick the unit (L or mL). The calculator converts mL to liters automatically.
- Adjust the decimal places if needed to control rounding in your final answer.
- Click Calculate to see your molarity in mol/L, along with a brief summary of the inputs used.
Formula and calculation steps
When moles are known
If you already know the moles of solute (n) and the total solution volume in liters (V), the calculation is straightforward:
- Convert volume to liters if necessary (for example, 250 mL = 0.250 L).
- Apply M = n / V.
When only mass is known
If you know the mass of solute (m, in grams) and its molar mass (MM, in g/mol):
- First compute moles: n = m / MM.
- Convert volume to liters.
- Then compute M = n / V.
Example: Dissolving 5.00 g of NaCl (MM ? 58.44 g/mol) to make 250 mL of solution. First, n = 5.00 / 58.44 ? 0.0856 mol. Convert 250 mL to 0.250 L. Then M = 0.0856 / 0.250 = 0.342 M.
Why use this Molarity Calculator?
- Flexible inputs: work with moles directly or calculate them from mass and molar mass.
- Automatic unit conversion: enter volume in liters or milliliters.
- Adjustable precision: set the number of decimal places to match lab reporting standards.
- Clear readout: see the final M value plus a concise summary of your inputs and the formula used.
Common pitfalls to avoid
- Forgetting to convert mL to liters. Molarity requires liters, so 1,000 mL equals 1.00 L.
- Using the wrong molar mass. Always verify the chemical formula, including hydrates and counterions.
- Confusing molarity with molality. Molality (m) uses kilograms of solvent, not liters of solution, and is temperature independent.
- Rounding too early. Keep extra significant figures in intermediate steps, then round the final answer as needed.
Applications of molarity
Molarity is essential for preparing standard solutions, carrying out acid–base and redox titrations, and determining reaction stoichiometry. It enables you to convert measured volumes into moles using n = M × V, which is particularly handy when calculating limiting reagents or predicting theoretical yields. In quality control and education, consistent use of molarity helps ensure reproducibility and clear communication across teams and reports.
Tips for accurate results
- Measure volumes with calibrated glassware (volumetric flasks, pipettes) for best accuracy.
- Account for temperature effects if high precision is required; solution volume can change with temperature.
- If working with hydrates or mixtures, confirm the exact composition before calculating molar mass.
- Document the number of significant figures and units in your final report.
Whether you are setting up a titration, preparing buffer solutions, or teaching concentration concepts, this Molarity Calculator provides a fast, reliable path from raw inputs to a clean, properly rounded molarity value in mol/L.