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Alcohol Dilution Calculator

Calculate alcohol dilution, fortification, and blending

🍷Common ABV Levels

Beer3-12%
Wine11-15%
Fortified Wine15-20%
Liqueurs15-30%
Spirits40-50%
Cask Strength50-65%

⚠️Safety Notes

• Always add water to alcohol, not alcohol to water
• Use distilled water for best results
• Allow mixture to settle before final measurement
• Temperature affects ABV measurements

Alcohol Dilution Calculator: Calculate Water Addition and Fortification

Table of Contents - Alcohol Dilution

How to Use This Calculator - Alcohol Dilution

The calculator has two modes, selectable via buttons at the top: "Dilute with Water" and "Fortify with Alcohol."

Dilute with Water mode: Use this when you want to lower the ABV (alcohol by volume) of a spirit by adding water. Enter three values: Current Volume (in ml), Current ABV (as a percentage), and Target ABV (the lower percentage you're aiming for). Click "Calculate Dilution" to see how much water to add.

Fortify with Alcohol mode: Use this when you want to raise the ABV by adding high-proof alcohol. Same three inputs, but your Target ABV must be higher than your Current ABV. Click "Calculate Fortification" to see how much 95% alcohol to add.

Results display in a purple results box showing: the amount of water or alcohol to add (in ml), the final volume, and either the dilution ratio (for dilution) or proof increase (for fortification). A "Calculation Details" section shows starting ABV, target ABV (both in percentage and proof), original volume, and pure alcohol content.

Below the calculator, reference panels show common ABV levels for various beverages (beer at 3-12%, wine at 11-15%, spirits at 40-50%, cask strength at 50-65%) and safety notes about proper dilution technique.

The calculator will show an error if you enter invalid combinations—like trying to dilute to a higher ABV or fortify to a lower one.

The Core Principle: Conservation of Alcohol

When you add water to spirits, the alcohol doesn't disappear or multiply. The total amount of pure alcohol stays constant. What changes is its concentration—the percentage of the total volume that's alcohol.

If you have 750 ml of 60% ABV whiskey, you have 450 ml of pure alcohol (750 × 0.60). Adding 250 ml of water gives you 1,000 ml total volume, still containing 450 ml of alcohol. The new ABV is 450 ÷ 1,000 = 45%.

This conservation principle makes dilution calculations straightforward: multiply current volume by current ABV to get pure alcohol content, then divide by target ABV to find the required final volume. The difference between final volume and current volume is how much water to add.

Fortification works the same way in reverse, though it's more complex because the alcohol you're adding has its own volume that contributes to the final total.

How to Calculate Dilution Manually

The dilution formula:

Water to Add = (Current Volume × Current ABV ÷ Target ABV) - Current Volume

Or equivalently:

Final Volume = Current Volume × (Current ABV ÷ Target ABV) Water to Add = Final Volume - Current Volume

Example: Diluting cask-strength whiskey

You have 700 ml of whiskey at 58% ABV. You want to bring it down to 46% ABV for drinking.

Step 1: Calculate pure alcohol content. 700 ml × 0.58 = 406 ml of pure alcohol

Step 2: Calculate required final volume. 406 ml ÷ 0.46 = 882.6 ml

Step 3: Calculate water needed. 882.6 - 700 = 182.6 ml of water

Add approximately 183 ml of water.

The fortification formula:

For adding 95% alcohol to raise ABV:

Alcohol to Add = Current Volume × (Target ABV - Current ABV) ÷ (95 - Target ABV)

Example: Fortifying wine

You have 750 ml of wine at 12% ABV. You want to fortify it to 18% ABV using grape spirit at 95% ABV.

Alcohol to Add = 750 × (18 - 12) ÷ (95 - 18) Alcohol to Add = 750 × 6 ÷ 77 = 58.4 ml

Add approximately 58 ml of 95% alcohol.

Real-World Applications

Spirits production. Distilleries routinely dilute cask-strength spirits (often 60-70% ABV) down to bottling strength (typically 40-46% ABV). Precise calculation ensures consistent product and regulatory compliance.

Home bartending. Cocktail enthusiasts who buy cask-strength or overproof spirits often dilute them to standard strength for mixing. Proper dilution preserves flavor while adjusting potency.

Wine fortification. Making port, sherry, or vermouth involves adding grape spirit to wine. The target ABV affects both flavor profile and stability. Fortified wines typically range from 15-22% ABV.

Homebrew adjustments. Home distillers and winemakers use dilution calculations to hit target ABVs for their products. Getting this wrong means products that are either too harsh or too weak.

Proofing for legal compliance. Commercial spirits must meet specific proof requirements for their category. "Bonded" whiskey must be exactly 100 proof (50% ABV). Calculations must be precise for regulatory compliance.

Scenarios People Actually Run Into

The "it tastes wrong" problem. You diluted your whiskey to 40% ABV as calculated, but it tastes different than commercial 40% ABV whiskey. This is real—rapid dilution at home differs from the slow, controlled dilution at distilleries, where spirits may rest for weeks after water addition to integrate.

The contraction confusion. When you mix alcohol and water, the resulting volume is slightly less than the sum of the two volumes (due to molecular interactions). 500 ml of alcohol plus 500 ml of water doesn't equal 1,000 ml—it's closer to 970 ml. For home use this is negligible, but commercial calculations account for it.

The temperature factor. ABV measurements assume a standard temperature (usually 20°C/68°F). Spirits measured cold read higher ABV than the same liquid measured warm. If precision matters, temperature-correct your measurements.

The "I added too much water" recovery. You overshot your target ABV. The only fix is adding more alcohol—but adding cask-strength back doesn't perfectly reverse water addition due to those volume contraction effects. You can get close, but it's easier to be conservative with water.

The proof versus ABV confusion. American proof is twice the ABV (80 proof = 40% ABV). British proof is different (uses a historical system). The calculator works in ABV; convert proof to ABV first.

Trade-Offs and Decisions People Underestimate

Speed versus integration. Quick dilution is convenient but can produce harsh results. Professional distillers often add water gradually over days or weeks, allowing the liquid to "marry" and the flavor to smooth out. Home dilution works, but the product may benefit from resting.

Water quality matters. Tap water contains minerals and chlorine that affect flavor. Distilled water is neutral but some argue it produces flat results. Many distillers prefer soft spring water. The calculator doesn't account for water quality, but you should.

The 95% assumption for fortification. The calculator assumes you're adding 95% ABV alcohol for fortification. If you're using something weaker (like brandy at 40%), the calculation is wrong. You'd need to adjust the formula for your actual alcohol strength.

Dilution ratio versus actual volumes. The calculator shows both water to add and dilution ratio. For small batches, the ratio might be more practical (dilute at 1.26:1). For large batches, absolute volumes (add 182.6 ml) are clearer.

Target ABV selection. Lower isn't always better. Many spirits are designed for specific ABV ranges where their flavors balance. Diluting below the intended range can make them taste thin or unbalanced.

Common Mistakes and How to Recover

Diluting when you meant to fortify (or vice versa). If you're in the wrong mode, the calculator will show an error (target ABV must be lower than current for dilution, higher for fortification). But if you physically added the wrong thing—water when you needed alcohol—your only recourse is starting over or adding a lot of high-proof spirit.

Measuring by weight instead of volume. Alcohol is less dense than water. If you measure 100g of water thinking it's 100ml, you're slightly off. For alcohol, the error is larger. Measure by volume unless you're specifically converting with density factors.

Using incorrect current ABV. If your starting spirit isn't what you think it is (maybe it was already diluted, or the label is wrong), all calculations will be off. When precision matters, verify ABV with an alcoholmeter.

Forgetting about proof contraction. For home use, this 3% volume loss from mixing is usually ignorable. For commercial production or very precise work, it matters. The calculator doesn't account for it.

Adding water too fast. Dumping water in all at once can cause "bruising"—creating haze or affecting flavor. Add water gradually and stir gently. This isn't a calculation error but an execution one.

Related Topics

Alcohol proof history. The term "proof" comes from an old British test: gunpowder soaked in the spirit would ignite if the spirit was strong enough, "proving" its strength. This corresponded roughly to 57% ABV, which became "100 proof" in the British system.

Louching. Some spirits (absinthe, ouzo, pastis) turn cloudy when diluted with water. This "louche" or "ouzo effect" happens because essential oils dissolved in alcohol become insoluble as ABV drops. It's normal and expected for these spirits.

Chill filtration. Whiskey producers sometimes chill-filter their product to remove compounds that would cause haziness when diluted or chilled. This affects the calculation—chill-filtered spirits don't louche, but some argue filtration removes flavor.

Blending calculations. Mixing two spirits of different ABVs requires similar math to fortification. The Pearson square method helps calculate ratios to hit a target ABV when blending.

Alcohol contraction tables. Official tables published by regulatory bodies give exact contraction values for alcohol-water mixtures at various concentrations and temperatures. These are used for precise commercial calculations.

How This Calculator Works

Dilution mode:

The calculator takes Current Volume (V₁), Current ABV (C₁), and Target ABV (C₂).

Pure alcohol = V₁ × (C₁ ÷ 100) Final volume = Pure alcohol ÷ (C₂ ÷ 100) Water to add = Final volume - V₁ Dilution ratio = Final volume ÷ V₁

Fortification mode:

The calculator assumes you're adding 95% ABV alcohol.

Alcohol to add = V₁ × (C₂ - C₁) ÷ (95 - C₂) Final volume = V₁ + Alcohol to add Proof increase = (C₂ - C₁) × 2

The results section also shows the starting values, proof equivalents (ABV × 2), and pure alcohol content for reference.

Validation prevents impossible calculations: you can't dilute to a higher ABV or fortify to a lower one.

All calculations happen in your browser. No data is sent anywhere.

FAQs

Why is my target ABV limited in dilution mode?

Target ABV must be lower than current ABV when diluting—you can't make something stronger by adding water. If you need to increase ABV, switch to fortification mode.

What's the difference between ABV and proof?

ABV (alcohol by volume) is the percentage of pure alcohol in the liquid. US proof is simply ABV × 2 (so 40% ABV = 80 proof). The calculator works in ABV; multiply by 2 if you need proof.

Does water quality affect the calculation?

Not the math, but the result. Distilled water adds nothing but H₂O. Tap water contributes minerals and potential off-flavors. Many people prefer filtered or spring water for diluting spirits they plan to drink.

Why does the calculator assume 95% alcohol for fortification?

95% ABV (190 proof) is typical for neutral grain spirit or grape spirit used in fortification. If you're using something weaker, the calculation will underestimate how much you need.

Can I dilute in stages?

Yes. You can dilute partway, taste, then continue. The math works for any starting point. Just recalculate from your new volume and ABV.

Why might my diluted spirit taste different than expected?

Commercial spirits are often diluted slowly over time, allowing flavors to integrate. Home dilution is instant. Try letting your diluted spirit rest for a few days before judging.

What's the dilution ratio used for?

It tells you the proportion of final volume to original volume. A ratio of 1.26:1 means your final volume is 1.26 times your starting volume. Useful for scaling to different batch sizes.

Is there a minimum ABV I should dilute to?

Functionally, no. But spirits below about 20% ABV may have stability issues (microbial growth becomes possible). For long-term storage, stay above 20%. For immediate drinking, dilute to your preference.