Calculators
Molarity Calculator
Solve molarity, moles, volume, or solute mass using M = n/V.
Molarity Calculator tool
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About This Tool
Molarity describes how many moles of dissolved solute are present per liter of final solution. It is one of the most common ways to express solution concentration in chemistry. This calculator rearranges the core relationship M = n/V so you can solve for molarity, amount of solute, final solution volume, or—when molar mass is known—the mass of solute needed. It keeps the distinction between solution volume and solvent volume explicit because confusing those quantities is a common source of preparation errors.
How To Use It
- Choose whether you want to solve for solute mass, molarity, moles, or final solution volume.
- Enter the requested quantities. Zero solute amount, concentration, or mass is allowed when the final solution volume is positive; solution volume, molar mass, and divisors must be positive. The interface converts milliliters to liters internally where needed.
- For a mass calculation, enter a verified molar mass in grams per mole for the exact chemical form you are using.
- Read and copy the result, then apply appropriate significant figures for your measured data.
Examples
Find molarity
0.50 mol of solute in a final solution volume of 250 mL is 0.50/0.250 = 2.0 mol/L.
Prepare sodium chloride solution
For 200 mL of 0.50 M solution using a molar mass of 58.44 g/mol, required mass is 0.50 × 0.200 × 58.44 = 5.844 g.
Find required volume
If 0.10 mol should make a 0.25 M solution, V = n/M = 0.10/0.25 = 0.40 L, or 400 mL final solution volume.
Useful Notes
Core molarity equation
Molarity M is amount n divided by final solution volume V in liters: M = n/V. Therefore n = MV and V = n/M. The standard molarity unit mol/L is also written M in chemistry contexts.
Calculating solute mass
When molar mass Mm is known, mass m = n × Mm. Combining this with n = MV gives m = M × V × Mm. Use liters for V, mol/L for M, and g/mol for molar mass to obtain grams.
Final solution volume is not solvent volume
A target such as 200 mL of solution means the prepared solution should have a final total volume of 200 mL. It does not generally mean adding the solute to exactly 200 mL of solvent, because dissolving and mixing can change total volume.
Molar mass must match the chemical form
Hydrated and anhydrous salts, different molecular species, and compounds with similar names can have different molar masses. Verify the formula and molar mass from an appropriate trusted source before using a mass result.
Precision and significant figures
The calculator retains useful numerical precision, but experimental reporting should reflect the precision of the measured mass, volume, concentration, and molar mass. Do not imply more laboratory certainty simply because a calculator displays extra digits.
What this ideal calculation does not model
The equations describe nominal amount-per-volume concentration. They do not account for purity, assay percentage, solution non-ideality, temperature-dependent volumetric expansion, chemical reaction, dissociation equilibria, activity coefficients, or instrument uncertainty.
FAQ
What is the formula for molarity?
M = n/V, where M is molarity in mol/L, n is moles of solute, and V is final solution volume in liters.
How do I calculate grams needed for a molar solution?
Use grams = molarity × final volume in liters × molar mass in g/mol.
Should I enter solvent volume or solution volume?
Use the final total solution volume. For laboratory preparation, solute is typically dissolved and then the solution is brought to the target final volume.
Can this calculator find molar mass from a formula?
No. It intentionally requires a verified molar mass for mass calculations rather than maintaining an atomic-weight parser/table in this tool.
Does 1 M always mean 1 mole in 1 liter of solvent?
No. It means 1 mole of solute per 1 liter of final solution, not per liter of solvent.