Molarity and Dilution Calculator

Molarity is how chemists describe the strength of a solution: how many moles are dissolved in each liter. This calculator solves molarity problems either way round, and plans dilutions: tell it the stock you have and the solution you want, and it says how much stock to measure out and how much water to add.

How to Use It

1. Choose Molarity or Dilution.
2. For molarity, pick what to Find and enter the other two values with their units.
3. For a dilution, enter the Stock Concentration, the Target Concentration and the Final Volume you want.
4. Press Calculate.

How It Works

Molarity is moles of solute per liter of solution:

Rearranged, $n = MV$ and $V = \frac{n}{M}$, with V in liters.

Diluting adds solvent but not solute, so the moles before and after are equal:

The water to add is $V_2 - V_1$, and the dilution factor is $\frac{C_1}{C_2}$.

Worked Example

0.5 mol of solute dissolved to make 2 L of solution:

To make 250 mL of 0.5 M solution from 2 M stock:

Measure out 62.5 mL of stock and add water up to 250 mL (187.5 mL of water), a 4× dilution.

Tips and Common Mistakes

• Use liters of solution. 250 mL is 0.25 L, and it’s the total volume, not the water added.
• Convert grams to moles first. Divide the mass by the molar mass from the formula.
• Fill to the mark. Dissolve the solute, then add water up to the final volume, rather than adding a measured amount of water.
• Keep concentration units matching in C₁V₁ = C₂V₂; the calculator converts M and mM for you.
• Add acid to water, not water to acid, when diluting a strong acid in the lab.