Alcohol Dilution Calculator
Calculate how much water to add to dilute spirits, liqueurs, or any alcoholic solution to your desired ABV. Perfect for proofing down spirits, making cocktail bases, or adjusting homebrew strength. See also our Alcohol by Volume Calculator and mL to Grams Converter.
How to Use the Alcohol Dilution Calculator
This calculator determines exactly how much water you need to add to reduce the alcohol content of a spirit or solution to your desired strength. It is commonly used by distillers to proof down spirits from barrel strength to bottling strength, by homebrewers adjusting their final product, and by bartenders creating cocktail bases at specific ABV levels.
Enter the current ABV percentage of your spirit (for example, 40% for standard vodka or 60% for cask-strength whiskey). Then enter your target ABV — the strength you want to achieve after dilution. Input the current volume of spirit you have and select the appropriate unit (milliliters, liters, fluid ounces, or gallons). Click Calculate to see how much water to add, the resulting final volume, and the US proof equivalent.
Important note: this calculator assumes ideal dilution where volumes are additive. In reality, mixing alcohol and water produces a slight volume contraction (the final volume is slightly less than the sum of the two volumes). For most practical purposes, this difference is negligible (less than 3%), but professional distillers may need to account for it using TTB (Alcohol and Tobacco Tax and Trade Bureau) gauging tables.
Dilution Formula
Water to Add = Current Volume × ((Current ABV / Target ABV) - 1)
Final Volume = Current Volume + Water to Add
US Proof = ABV × 2
The formula is derived from the principle of conservation of alcohol: the amount of pure alcohol before and after dilution must be equal. If you have V₁ volume at C₁ concentration and want to reach C₂ concentration, the pure alcohol is V₁ × C₁. After adding water (volume W), the new concentration is V₁ × C₁ / (V₁ + W) = C₂. Solving for W gives us: W = V₁ × (C₁/C₂ - 1).
US Proof is simply double the ABV percentage. This system dates back to the 18th century when "proof spirit" was defined as spirit that would ignite gunpowder — approximately 50% ABV or 100 proof. The UK historically used a different proof system (Sikes) where 100 proof was 57.15% ABV, but this has been largely replaced by ABV in modern usage.
Example Calculation
Let us calculate how much water to add to dilute 750ml of 40% ABV vodka down to 25% ABV:
Step 1: Water to Add = 750 × ((40 / 25) - 1)
Step 2: Water to Add = 750 × (1.6 - 1) = 750 × 0.6 = 450 ml
Step 3: Final Volume = 750 + 450 = 1,200 ml
Step 4: Proof = 25 × 2 = 50° proof
Result: Add 450 ml of water to 750 ml of 40% vodka to get 1,200 ml at 25% ABV (50 proof).
Verification: 750 ml × 40% = 300 ml pure alcohol. 1,200 ml × 25% = 300 ml pure alcohol. The amount of pure alcohol is preserved, confirming the calculation is correct.
Common Dilution Reference Table
| Starting ABV | Target ABV | Water per 1L | Final Volume | Common Use |
|---|---|---|---|---|
| 95% | 40% | 1,375 ml | 2,375 ml | Neutral spirit to vodka |
| 65% | 40% | 625 ml | 1,625 ml | Cask strength to bottle |
| 60% | 43% | 395 ml | 1,395 ml | Barrel proof whiskey |
| 40% | 25% | 600 ml | 1,600 ml | Liqueur base |
| 40% | 20% | 1,000 ml | 2,000 ml | Low-ABV cocktail base |
| 20% | 12% | 667 ml | 1,667 ml | Wine-strength dilution |
| 96% | 60% | 600 ml | 1,600 ml | Limoncello base |
| 50% | 30% | 667 ml | 1,667 ml | Infusion dilution |
Best Practices for Diluting Spirits
When diluting spirits, always use distilled or filtered water. Tap water can contain minerals and chlorine that affect flavor. Add water slowly and stir gently to avoid creating air bubbles. For best results, let the diluted spirit rest for at least 24 hours before tasting, as the water and alcohol molecules need time to fully integrate — this is called "marrying" and can take up to a week for optimal results.
Temperature matters when diluting. Both the spirit and water should be at room temperature (around 20°C/68°F) for accurate measurements. Cold liquids are denser and will give slightly different volumes. Professional distillers measure at exactly 20°C and use correction tables for other temperatures. If you are diluting a large batch, add the water in stages and measure the ABV with a hydrometer between additions.
Be aware of the "louche effect" — when diluting spirits that contain essential oils (like absinthe, ouzo, or pastis), the liquid may turn cloudy as oils come out of solution below a certain ABV threshold (typically around 30%). This is normal and expected for these spirits. For clear spirits like vodka or gin, cloudiness after dilution may indicate impurities.
Frequently Asked Questions
Can I use tap water to dilute spirits?
While tap water works in a pinch, distilled or reverse-osmosis filtered water is recommended. Tap water contains minerals (calcium, magnesium) and chlorine that can affect flavor and potentially cause cloudiness. Spring water with low mineral content is also acceptable.
Why does mixing alcohol and water produce heat?
When ethanol and water molecules mix, they form hydrogen bonds that release energy as heat (exothermic reaction). This also causes a slight volume contraction — 1L of alcohol plus 1L of water produces slightly less than 2L of solution. This is why professional distillers use weight-based measurements rather than volume.
What is the difference between ABV and proof?
In the US, proof is simply ABV multiplied by 2. So 40% ABV = 80 proof. This system originated from a historical test where gunpowder soaked in spirit would ignite if the spirit was at least 50% alcohol (100 proof). The UK formerly used a different proof system but now uses ABV exclusively.
How do I increase the ABV of a spirit?
You cannot increase ABV by adding anything — you can only concentrate it through distillation or freeze concentration (removing water as ice). To blend up to a higher ABV, you would need to add a higher-proof spirit. This calculator only handles dilution (reducing ABV).
How long should I let diluted spirits rest before drinking?
Allow at least 24 hours for the water and alcohol to fully integrate (marry). For best results, wait 3-7 days. Freshly diluted spirits can taste harsh or disjointed because the molecules have not yet reached equilibrium. Professional distillers often let proofed spirits rest for weeks before bottling.
Is this calculator accurate for wine and beer dilution?
The formula works for any alcohol-water solution, but diluting wine or beer with water will significantly affect flavor, carbonation, and mouthfeel. It is more common to blend wines of different strengths rather than adding water directly. For beer, dilution is sometimes done with de-aerated water to avoid oxidation.