Last updated: July 2, 2026
Molarity Calculator
Creators
Dharmendra SinghReviewers
Creators
Dharmendra SinghReviewers
Quick Answer
Molarity is the concentration of a solution expressed as moles of solute per litre of solution (mol/L, symbol M). It is calculated as M = n / V, or from mass as M = mass / (molar mass × volume). For example, dissolving 58.44 g of NaCl to make 1 L gives a 1 M solution.
Molarity equals the number of moles of solute divided by the volume of the solution in litres, and is measured in moles per litre, written as M.
Key Takeaways
- Molarity (M) equals moles of solute divided by litres of solution: M = n / V.
- From mass, use M = mass / (molar mass × volume).
- Molarity has units of mol/L, abbreviated M; a 1 M solution has 1 mole per litre.
- Always use the final solution volume in litres, not the solvent volume.
- Molarity is temperature-dependent because solution volume changes with temperature.
Creators
Dharmendra SinghReviewers
Creators
Dharmendra SinghReviewers
Formula
M = n / V = mass / (molar mass × volume)
Where:
- M=Molarity (molar concentration)(mol/L)
- n=Amount of solute(mol)
- V=Volume of solution(L)
- m=Mass of solute(g)
- M_w=Molar mass of solute(g/mol)
Worked Examples
Sodium chloride (NaCl) — 1 M standard
Prepare a 1 molar solution of table salt.
- 1Convert mass to moles: n = 58.44 g ÷ 58.44 g/mol = 1 mol.
- 2Divide moles by volume: M = 1 mol ÷ 1 L = 1 mol/L.
- 3The solution is 1 M (one molar).
Glucose (C₆H₁₂O₆) — 0.5 M
Dissolve glucose in a 2-litre solution.
- 1Convert mass to moles: n = 180.16 g ÷ 180.16 g/mol = 1 mol.
- 2Divide by volume: M = 1 mol ÷ 2 L = 0.5 mol/L.
- 3The solution is 0.5 M.
Potassium permanganate (KMnO₄) — 0.4 M
A small volume, moderately concentrated solution.
- 1Convert mass to moles: n = 15.8 g ÷ 158.03 g/mol ≈ 0.1 mol.
- 2Divide by volume: M = 0.1 mol ÷ 0.25 L = 0.4 mol/L.
- 3The solution is 0.4 M.
Introduction
Molarity is the most common way chemists express the concentration of a solution. It measures how many moles of solute are dissolved in one litre of solution, with units of mol/L — universally abbreviated as M. This calculator finds molarity from the mass of your solute, its molar mass, and the solution volume, and also reports the number of moles and the mass concentration (g/L). The definition follows the IUPAC amount-of-substance concentration convention used across analytical and physical chemistry.
What is molarity?
Molarity (M) is the amount of solute, measured in moles, per litre of solution (not per litre of solvent). The formula is M = n / V, where n is moles of solute and V is the volume of the solution in litres. Because it is defined per litre of final solution, molarity already accounts for any volume change that occurs on mixing. It is the standard concentration unit for titrations, reaction stoichiometry, and preparing reagents.
1 M = 1 mole of solute per litre of solution.
Molarity depends on temperature because volume changes with temperature.
Use molarity for reaction calculations; use molality when temperature independence matters.
Related concentration units include normality and mole fraction.
The molarity formula explained
To use the formula you usually need moles, which you obtain from mass and molar mass: n = m / M_w. Substituting gives the practical working equation M = m / (M_w × V). So to raise concentration you either add more solute (increase m) or reduce the volume V. The calculator performs both steps for you and additionally reports mass concentration (g/L = molarity × molar mass).
Always convert your volume to litres before dividing. 500 mL = 0.5 L, and 250 mL = 0.25 L.
How to calculate molarity step by step
Follow these steps to find the molarity of any solution:
Find the molar mass of the solute (sum of atomic masses) — or use our molar mass calculator.
Weigh the solute and record its mass in grams.
Convert mass to moles: n = mass ÷ molar mass.
Measure the total solution volume and convert it to litres.
Divide moles by litres: M = n ÷ V.
Check the result against a reference range to confirm it is reasonable.
Common molarity reference values
The table below lists typical molar masses and the mass needed to prepare a 1 M solution in 1 litre. Scale the mass up or down for other volumes and concentrations.
| Compound | Formula | Molar mass (g/mol) | Mass for 1 L of 1 M (g) |
|---|---|---|---|
| Sodium chloride | NaCl | 58.44 | 58.44 |
| Glucose | C₆H₁₂O₆ | 180.16 | 180.16 |
| Sodium hydroxide | NaOH | 40.00 | 40.00 |
| Hydrochloric acid | HCl | 36.46 | 36.46 |
| Potassium permanganate | KMnO₄ | 158.03 | 158.03 |
| Copper(II) sulfate | CuSO₄ | 159.61 | 159.61 |
Molarity vs. molality and other units
Molarity (mol per litre of solution) is easy to measure with volumetric glassware but changes with temperature. Molality (mol per kilogram of solvent) is temperature-independent and preferred for colligative-property work such as boiling-point elevation. Normality expresses equivalents per litre and is common in acid–base and redox titrations. Choosing the right unit avoids errors when you scale or heat a solution.
Molarity (M): mol solute / L solution — general purpose.
Molality (m): mol solute / kg solvent — temperature independent.
Normality (N): equivalents / L — titrations.
Mole fraction: dimensionless ratio of moles.
Practical tips and common mistakes
Accurate molarity starts with accurate measurement. A frequent mistake is dividing by the solvent volume instead of the final solution volume — always dissolve, then top up to the mark in a volumetric flask. Another is forgetting to convert millilitres to litres. For guidance on preparing standards, see the LibreTexts solutions chapter.
For dilutions of an existing stock, use M₁V₁ = M₂V₂ rather than recomputing from mass.
Quick Reference Card
Molarity — Quick Reference
Quick reference • Molarity Calculator
M = n / V = mass / (molar mass × volume)Valid range: 0 M (pure solvent) to solubility limit; lab reagents are typically 0.01–12 M
Common Values
⚠ Watch Out
- •Divide by the final solution volume, not the solvent volume.
- •Convert millilitres to litres before calculating (500 mL = 0.5 L).
- •Molarity changes with temperature; report the temperature for precise work.
- •Use the correct molar mass, including waters of hydration if present.
Pro Tips
- →For diluting a stock solution, use M₁V₁ = M₂V₂ instead of starting from mass.
- →Prepare standards in a volumetric flask and top up to the calibration mark.
- →Mass concentration (g/L) = molarity × molar mass — handy for balances.
- →Keep significant figures consistent with your least precise measurement.
FAQs
What is molarity in simple terms?
Molarity is the number of moles of a dissolved substance (solute) per litre of solution. A 1 M solution contains 1 mole of solute in every litre. It is written with the unit mol/L or the capital letter M.
How do I calculate molarity from grams?
First convert grams to moles by dividing by the molar mass (n = mass ÷ molar mass). Then divide the moles by the solution volume in litres (M = n ÷ V). This calculator does both steps automatically.
Is molarity the same as concentration?
Molarity is one specific way of expressing concentration — moles per litre. Concentration is a broader term that also includes mass concentration (g/L), molality (mol/kg), normality, and percent solutions.
Why does molarity change with temperature?
Molarity is defined per litre of solution, and liquid volume expands or contracts with temperature. Because the volume changes while the number of moles stays constant, the molarity shifts slightly. Molality (mol per kg of solvent) avoids this because mass does not change with temperature.
What is the difference between molarity and molality?
Molarity is moles of solute per litre of solution; molality is moles of solute per kilogram of solvent. Molarity is convenient for volumetric work but temperature-dependent, whereas molality is temperature-independent and preferred for colligative properties.
How do I make a solution of a specific molarity?
Multiply the desired molarity by the desired volume in litres to get the moles needed, then multiply by the molar mass to get the mass to weigh out. Dissolve that mass in some solvent and top up to the final volume in a volumetric flask.