Use this Alcohol Dilution Calculator to estimate how much water or weaker alcoholic liquid to add to a stronger alcohol to reach a target alcohol by volume (ABV). It also estimates the final volume and mixing ratio.

Important: This calculator uses simplified volume-based dilution math. It is suitable for general planning and educational calculations, not professional proofing, commercial labeling, taxation, laboratory analysis, or regulatory compliance.

Alcohol Dilution Formula

The calculator assumes the amount of ethanol remains the same before and after dilution:

V_sA + V_wB = (V_s + V_w)C

Where:

• V_s = starting volume of stronger alcohol
• A = starting ABV
• V_w = volume of water or weaker alcohol to add
• B = ABV of the weaker liquid
• C = target ABV

Solving for the amount of weaker liquid to add:

V_w = V_s × (A − C) ÷ (C − B)

If plain water is used:

B = 0% ABV

Worked Example

Suppose you have 500 mL of 60% ABV alcohol and want to dilute it to 40% ABV using water.

Here:

• Starting volume = 500 mL
• Starting ABV = 60%
• Water ABV = 0%
• Target ABV = 40%

Apply the formula:

Water to add = 500 × (60 − 40) ÷ (40 − 0)

Water to add = 250 mL

The simplified estimated final volume is:

500 + 250 = 750 mL

The mixing ratio is therefore:

500 : 250 = 2 : 1

So the calculator estimates that 250 mL of water should be added to 500 mL of 60% ABV alcohol to produce an approximately 40% ABV mixture.

Using a Weaker Alcohol Instead of Water

The added liquid does not have to be 0% ABV. If a weaker alcoholic liquid is used, its alcohol content must also be included.

For example, mixing equal volumes of 60% ABV and 20% ABV liquids gives a simplified target of 40% ABV:

V_w = V_s × (60 − 40) ÷ (40 − 20) = V_s

Therefore, under the simplified model, equal volumes are required.

Target ABV Requirement

For dilution with a weaker liquid, the target must normally fall between the two starting strengths:

Weak-liquid ABV < target ABV < strong-liquid ABV

For example, adding water to 60% ABV alcohol can reduce it to 40%, but it cannot increase it to 70%.

Important Notes

• ABV means alcohol by volume. In U.S. distilled spirits terminology, proof is twice the percentage ABV; for example, 40% ABV equals 80 proof.
• The calculator assumes the entered ABV values are accurate.
• The displayed final volume is approximate. Ethanol and water mixtures do not behave as perfectly additive volumes.
• Temperature can affect alcohol-volume and hydrometer measurements. Professional proofing uses temperature corrections and official alcohol-density or gauging tables.
• Sugars, flavorings, botanicals, and other dissolved substances can affect density-based alcohol measurements.
• Use only food-grade ingredients intended for consumption when making beverage calculations. Never assume laboratory, industrial, denatured, or cleaning alcohol is drinkable.
• High-strength ethanol is flammable. Keep concentrated alcohol away from flames, sparks, and other ignition sources.
• This calculator does not determine whether home dilution, production, labeling, sale, or possession is permitted under local law.
• Commercial producers and laboratories should use the applicable official proofing and measurement procedures instead of this simplified calculator.

Sources

• Alcohol and Tobacco Tax and Trade Bureau — Distilled Spirits, ABV and Proof
• Alcohol and Tobacco Tax and Trade Bureau — Distilled Spirits Gauging Manual
• World Health Organization — Ethanol Flammability and Storage Risks