Alcohol Dilution Calculator

Alcohol dilution follows the principle of conservation: the amount of pure alcohol remains constant before and after dilution. If you have 750 mL of liquid at 60% ABV, it contains 450 mL of pure ethanol. Diluting to 40% ABV requires a total volume of 450/0.40 = 1125 mL, meaning 375 mL of water must be added. The formula is: water = V1 * (C1/C2 - 1), where V1 is the initial volume, C1 is the initial concentration, and C2 is the target concentration. This assumes ideal mixing, which is approximately true for practical purposes. In reality, mixing water and ethanol is not perfectly additive. Due to hydrogen bonding between water and ethanol molecules, the mixed volume is slightly less than the sum of the individual volumes (about 3-4% contraction at typical spirit concentrations). Professional distillers account for this using the Alcohol and Tobacco Tax and Trade Bureau (TTB) gauging tables or the OIML Alcoholometric Tables. For home use, the simple formula is sufficient. The mixing of water and alcohol is exothermic (releases heat). When diluting high-proof spirits, the mixture will warm noticeably. This temperature change affects density measurements, so proof or ABV should be measured after the mixture returns to room temperature (typically 20 degrees C / 68 degrees F). Water quality matters for dilution. Distilled or reverse-osmosis water is preferred to avoid introducing minerals that could affect flavor or cause haziness. Tap water with high mineral content can cause clouding (louching) in some spirits, particularly those containing aromatic compounds like anise-flavored spirits. Proofing is the traditional term for measuring alcohol content. In the US, proof equals twice the ABV percentage (so 80 proof = 40% ABV). The UK historically used a different proof scale based on gunpowder ignition. Most countries now use ABV as the standard measurement.