Diluting to a target ABV
Whether you're proofing down a spirit, making a liqueur, or bringing a strong mead down to a sessionable strength, the arithmetic is the same. The amount of alcohol stays fixed, so adding water lowers the percentage:
Water to add = volume × (current ABV ÷ target ABV − 1)
For example, bringing 750 mL of a 60% spirit down to 40% takes 750 × (60 ÷ 40 − 1) = 375 mL of water.
Volume contraction: ethanol and water molecules pack together more tightly than either does alone, so mixing 500 mL of each gives slightly less than 1,000 mL. At spirit strength the effect is a percent or two, which leaves the result a little stronger than calculated. For exact proofing, add most of the water, rest the mixture, measure with an alcoholmeter at 20°C, and top up.
Working out the ABV of a blend or cocktail
The Blend ABV tab averages the strengths by volume:
ABV = Σ(volume × ABV) ÷ Σ(volume)
Use it for blending meads or wines of different strengths, or for estimating cocktail strength. For cocktails, include the water that melts from ice: stirred drinks gain about 20 to 25% in volume and shaken drinks about 25 to 30%.
Legal note
Distilling spirits at home is illegal without a license in many countries, including the United States and Canada. These calculators are intended for diluting and blending commercially produced spirits, liqueur making, and fermented beverages.
Looking for the strength of a fermented drink instead? Use the ABV calculator with your gravity readings.
Method and sources
- Dilution: water to add = volume × (current ABV ÷ target ABV − 1). The alcohol stays the same while the total volume grows.
- Blending: the blend's ABV is the volume-weighted average of each part.
- Limits: water and ethanol shrink slightly when mixed, so the true volume ends up a little under the sum of the parts and the ABV a touch higher than shown. At wine and cider strengths the difference is small. For spirits, check with an alcoholmeter after mixing.
Frequently asked questions
How much water do I add to dilute alcohol?
Water to add = current volume x (current ABV / target ABV - 1). Diluting 1 liter of 60% spirit to 40% takes 0.5 liters of water.
Why is my diluted spirit slightly stronger than expected?
Ethanol and water shrink a little when mixed, so the final volume is slightly less than the two volumes added together. Add water gradually and check with an alcoholmeter for exact proofing.
How do I calculate the ABV of a cocktail?
Multiply each ingredient's volume by its ABV, add those together, and divide by the total volume, including the water that melts from ice while shaking or stirring (typically 20 to 30%).