Apply the dilution law C1V1 = C2V2. Either work out the stock volume and water needed to reach a target final volume, or find the final volume you can reach from a stock volume you already have.
The unit is only used as a label on the results. Make sure the target concentration below uses the same unit.
A dilution factor of 10 means the final concentration is 1/10th of the stock concentration (a 1:10 dilution).
This calculation assumes an ideal mixing with no change in total volume when the solvent is added, which is accurate enough for dilute aqueous solutions but only approximate for concentrated or viscous ones.
Dilutions in GCSE and A-level Chemistry
Diluting a solution is one of the required practicals across UK GCSE and A-level Chemistry, from preparing a set of standard solutions for a calibration curve to diluting a stock reagent before a titration. The dilution law C1V1 = C2V2 holds because the amount of solute stays the same when solvent is added, only the volume changes. This tool works both ways: enter a stock concentration and a target final volume to find how much stock to measure out and how much water to add, or enter a stock volume you already have to find the final volume it reaches once diluted to a target concentration.
Typical dilution factors
| Dilution | Factor | Stock : final ratio |
|---|---|---|
| Light dilution | 2 | 1:2 |
| Common lab dilution | 10 | 1:10 |
| Diluted household bleach for surfaces | 10 to 50 | 1:10 to 1:50 |
| Serial dilution step | 10 | 1:10 per step |
| Trace analysis dilution | 100 or more | 1:100+ |
What this calculator cannot do
The dilution law assumes the total volume simply adds up when solvent is mixed in, which holds well for dilute aqueous solutions but is only an approximation for concentrated acids, alcohols, or other liquids where mixing can slightly change the total volume. The tool also will not let a target concentration equal or exceed the stock concentration, since adding solvent can only lower a concentration, never raise it; reaching a higher concentration would require removing solvent, for example by evaporation, which this calculator does not model.
Worked example
To prepare 250 mL of a 0.5 mol/L solution from a 2 mol/L stock, V1 = C2 x V2 / C1 = (0.5 x 250) / 2 = 62.5 mL of stock solution, topped up with 250 - 62.5 = 187.5 mL of water to reach the full 250 mL. Enter 2 mol/L as C1, 0.5 mol/L as C2, and 250 mL as the target volume above to check this. To work out a stock molarity from a mass of solute first, the Solution Concentration Calculator converts mass, molar mass, and volume into molarity, and the pH Calculator can then be used to check the pH of a diluted strong acid or base.