Molarity Calculator
Calculate molarity (concentration), moles of solute, or solution volume using M = n / V. Use the Dilution tab to apply the M₁V₁ = M₂V₂ equation.
Solve for:
Know the mass of solute instead of moles? (optional)
Entering both values fills in the Moles field automatically. Find the molar mass using the Molar Mass Calculator.
Quick examples:
Result
Use the dilution formula M₁V₁ = M₂V₂. Enter any three values to find the fourth.
Solve for:
What Is Molarity?
Molarity (symbol M) is the most common way to express the concentration of a solution in chemistry. It is defined as the number of moles of solute dissolved in exactly one litre of solution:
M = n / V
- M — molarity in mol/L (also written as mol·L⁻¹)
- n — moles of solute
- V — volume of solution in litres
Rearranging: n = M × V to find moles, and V = n / M to find volume.
Converting Grams to Moles
You often know the mass of solute you've weighed out rather than the number of moles. Convert using the molar mass (Mr) of the solute:
n = mass (g) / molar mass (g/mol)
Use the optional mass entry panel in the calculator above to do this in one step, or look up molar masses with the Molar Mass Calculator.
Serial Dilution and M₁V₁ = M₂V₂
When you dilute a stock solution to a lower concentration, the number of moles of solute stays constant. This gives the dilution equation:
M₁V₁ = M₂V₂
For example: diluting 25 mL of a 6.0 M HCl stock solution to 300 mL gives a final concentration of (6.0 × 25) / 300 = 0.5 M. Use the Dilution tab above to solve for any of the four variables.
For related stoichiometric calculations, see the Stoichiometry Calculator.
How to Use This Calculator
- Molarity tab: select which variable to solve for (M, n, or V), enter the known values, and click Calculate. If you only know the mass of solute, expand the optional mass panel and enter mass + molar mass to fill in moles automatically.
- Dilution tab: select which of the four dilution variables to find, enter the other three, and click Calculate.
Common Solution Concentrations
| Solution | Typical molarity | Notes |
|---|---|---|
| Saline (physiological) | 0.154 M NaCl | 0.9% w/v |
| Concentrated HCl | ~12 M | ~37% w/w |
| Concentrated H₂SO₄ | ~18 M | ~96% w/w |
| 1× PBS buffer | ~0.01 M phosphate | Common in biology |
| Seawater (NaCl equiv.) | ~0.6 M | Approximate |
Frequently Asked Questions
What is the difference between molarity and molality?
Molarity (M) is moles of solute per litre of solution and changes with temperature because liquids expand. Molality (m) is moles of solute per kilogram of solvent and is independent of temperature. Molarity is more common in lab settings; molality is preferred for colligative property calculations (boiling-point elevation, freezing-point depression).
What does 1 M mean in chemistry?
A 1 M (one molar) solution contains 1 mole of solute dissolved in enough solvent to make exactly 1 litre of solution. For sodium chloride (NaCl, molar mass 58.44 g/mol), a 1 M solution contains 58.44 grams of NaCl per litre.
How do I make a solution of known molarity?
Weigh out n = M × V moles of solute (convert to grams using molar mass), add it to a volumetric flask, dissolve in a small volume of solvent, then add solvent to the final target volume mark. Do not add solvent directly to the mark without first dissolving the solute.
Why does molarity depend on temperature?
Because molarity is defined as moles per litre of solution, and liquid volume changes with temperature. A solution prepared at 25 °C will have a slightly different molarity if measured at 4 °C. For precise work, specify the temperature or use molality instead.
What is the molarity of pure water?
Pure water has a molarity of approximately 55.5 mol/L (density ≈ 1 kg/L, molar mass = 18.015 g/mol → 1000/18.015 ≈ 55.5 mol/L). This value appears frequently in equilibrium expressions.
