Alcohol Dilution Calculator

Dilution formula for reducing alcohol by volume (ABV).

The formula:

• Water to add = Volume x (Current ABV / Target ABV - 1)

Example:

• You have 750 ml of spirit at 60% ABV
• You want to dilute to 40% ABV
• Water needed: 750 x (60/40 - 1) = 750 x 0.5 = 375 ml
• Final volume: 1,125 ml at 40% ABV

Common dilution scenarios:

• Cask strength whiskey (55-65%) to drinking strength (40-46%)
• High-proof spirits (75%) to bottling proof (40%)
• Homebrew spirits to desired strength

Notes:

• Use distilled or filtered water for best results.
• Mix slowly and let rest before measuring final ABV.
• Temperature affects density — measure at room temperature.
• There is slight volume contraction when mixing alcohol and water.

The formula works because diluting only adds water; the amount of pure alcohol in the bottle never changes. You’re spreading the same alcohol through more total liquid, which is why the math is a simple ratio of current strength to target strength. Distillers and home blenders use it to bring cask-strength spirits down to a drinkable proof without guesswork.

Two practical notes the numbers don’t show. Water and alcohol contract slightly when mixed, so the final volume comes out a touch less than the sum of the parts and the strength settles a hair higher than the formula predicts; measure after resting if you need precision. And diluting some spirits below about 46% can turn them cloudy, a harmless effect called louching, as oils that were dissolved in stronger alcohol drop out of solution. Distilled water added slowly gives the cleanest result, and letting the mix rest before a final measurement lets temperature and contraction settle.