Dilution Calculator
Stretching a Stock Solution Without Guesswork
Almost no one prepares a working solution from scratch every time — it's far more common to keep a concentrated stock on the shelf and dilute a small amount of it down as needed. The relationship that governs this is deceptively simple, but getting a variable wrong means either a solution that's too weak to work or too strong to be safe.
The Formula
C1 and V1 describe the concentrated stock before dilution; C2 and V2 describe the final, diluted solution. Because the total moles of solute don't change during dilution — only the volume does — this equation holds for any pair of consistent units.
Where This Calculation Matters
- Preparing lab reagents — scaling a concentrated stock down to a working concentration for an assay or reaction.
- Cleaning and disinfecting solutions — diluting a concentrate to a target percentage for safe, effective use.
- Pharmaceutical compounding — adjusting a stock drug concentration to a prescribed dose concentration.
- Serial dilutions — each step in a dilution series applies this same relationship in sequence.
Worked Examples
| Stock Concentration (C1) | Target Concentration (C2) | Target Volume (V2) | Stock Volume Needed (V1) |
|---|---|---|---|
| 10 mol/L | 1 mol/L | 1 L | 0.100 L |
| 5 mol/L | 0.5 mol/L | 0.5 L | 0.050 L |
In the first example, 100 mL of the 10 mol/L stock is brought up to a total of 1 L to reach 1 mol/L — the remaining 900 mL is solvent.
How to Use This Calculator
- Choose which value you're solving for — C1, V1, C2, or V2.
- Fill in the three known values among C1 – Initial Concentration (mol/L), V1 – Initial Volume (L), C2 – Final Concentration (mol/L), and V2 – Final Volume (L).
- Select Calculate to solve for the missing quantity.
Related Calculations
Working from a stock:diluent ratio like 1:4 instead of concentrations? The Dilution Ratio Calculator handles that form directly. To determine the stock concentration itself from a mass, start with the Molarity Calculator.