How It Works
This calculator works in 4 steps.
Pick the alcohol and basis
Select ethanol or isopropyl alcohol and % v/v or % w/w.
Enter the stock strength
Type the strength on the label.
Enter the target and final volume
Type the target % v/v and the final volume.
Read the volumes
The calculator returns alcohol volume and the instruction to fill to the final mark with water.
The Formula
The formula applies C₁V₁ = C₂V₂ in % v/v and fixes the final volume after mixing.
V_alc = %_target × V_final / %_stockV_water > V_final − V_alc (contraction)%v/v = %w/w × ρ_solution / ρ_alcohol- %_stock / %_target:
- Stock and target strength (% v/v)
- V_final:
- Final volume after mixing
- ρ:
- Densities at 20 °C
1 L of 70% v/v isopropyl alcohol from 99% stock needs 707.1 mL of alcohol, with water added to the 1,000 mL mark.
Conversion Table
The conversion table gives the alcohol volume for 1 L (33.8 US fl oz) of 6 common target strengths.
| Alcohol | Stock | Target | Alcohol per 1 L | Water step |
|---|---|---|---|---|
| Ethanol | 95% v/v | 70% v/v | 736.8 mL | Water to 1,000 mL |
| Ethanol | 99.5% v/v | 70% v/v | 703.5 mL | Water to 1,000 mL |
| Ethanol | 95% v/v | 80% v/v | 842.1 mL | Water to 1,000 mL |
| Isopropyl alcohol | 99% v/v | 70% v/v | 707.1 mL | Water to 1,000 mL |
| Isopropyl alcohol | 91% v/v | 70% v/v | 769.2 mL | Water to 1,000 mL |
| Ethanol | 70% v/v | 50% v/v | 714.3 mL | Water to 1,000 mL |
What Is the Alcohol Dilution Calculator?
The Alcohol Dilution Calculator is a tool that dilutes ethanol or isopropyl alcohol to a target strength, accounting for the concentration basis (% v/v or % w/w) and for volume contraction on mixing. The calculator returns the alcohol volume and a make-to-volume instruction.
Alcohol and water shrink when mixed, so adding 26.3 mL of water to 73.7 mL of 95% ethanol gives less than 100 mL. Measuring the alcohol and filling to the final mark with water gives the correct % v/v. Labels for spirits and solvents differ in basis, so the calculator asks whether the stock is % v/v or % w/w and converts with density tables.
Common Uses
There are 5 main uses of this calculator.
Surface disinfection
Labs and clinics prepare 70% alcohol for wiping surfaces.
Lab washes
Molecular labs prepare 70% and 80% ethanol for DNA washes.
Electronics cleaning
Technicians dilute isopropyl alcohol for board cleaning.
Extraction solvents
Herbal and lab extractions use set alcohol strengths.
Spirits blending
Distillers proof spirits down to bottling strength.