Percentage Dilution Calculator
Use this percentage dilution calculator to dilute a percent solution to a lower strength. Enter the stock %, the % you want, and the final volume — it returns how much stock and solvent to combine.
Enter the stock %, the % you want, and the final volume to get the stock and solvent to combine.
How to calculate a percent dilution
Diluting keeps the amount of solute the same and only adds solvent, so the percentages and volumes follow the dilution equation:
Solving for the stock volume gives:
V₂ is the final volume you want, and the solvent to add is V₂ − V₁. Keep the stock and target in the same kind of percent (both % w/v or both % v/v).
Worked example
Diluting a 10% stock to 2% to make 250 mL: V₁ = (2 × 250) ÷ 10 = 50 mL of stock plus 200 mL of solvent.
Common percent dilutions
A handful of percent-to-percent dilutions come up over and over — the target strengths are well established:
| Substance | Stock % | Common target % |
|---|---|---|
| Bleach (sodium hypochlorite) | 8.25% | 0.5–1% (surface disinfecting) |
| Isopropyl alcohol | 99% | 70% (disinfectant strength) |
| Formalin (formaldehyde) | 37% | 10% (histology fixative) |
| Ethanol | 95–100% | 70% (lab disinfection) |
| Hydrogen peroxide | 35% | 3% (household strength) |
Related tools
Working in parts per million instead? Use the ppm dilution calculator. To make a % w/v or % v/v solution from scratch, use the percent solution calculator, or work from a ratio with the dilution ratio calculator.
Frequently asked questions
›How do I calculate a percent dilution?
Use V₁ = (target % × V₂) ÷ stock %, where V₂ is the final volume you want. The solvent to add is V₂ − V₁. For example, diluting a 10% stock to 2% in 250 mL: V₁ = (2 × 250) ÷ 10 = 50 mL of stock plus 200 mL of solvent.
›What is the difference between % v/v and % w/v?
% v/v (volume/volume) is mL of liquid solute per 100 mL of solution — used for miscible liquids like alcohol. % w/v (weight/volume) is grams of solid solute per 100 mL. This dilution stays in whichever percent basis you start with; just keep the stock and target in the same type.
›Does the percent dilution formula depend on the units?
No — because it is a ratio of percentages times a volume, any consistent volume unit works, as long as the stock % and target % are the same kind of percent. The result comes out in the volume unit you enter.
›Is this percentage dilution calculator free?
Yes. It runs entirely in your browser, needs no sign-up, and never sends your numbers to a server.
›What percent should I dilute isopropyl alcohol to for disinfecting?
70% is the commonly recommended strength for surface and skin disinfection — counterintuitively, 70% outperforms 99% because the extra water slows evaporation, giving the alcohol more contact time to work.
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