Approximate water quantity for beverage dilution, with an explicit model limitation.
Starting values are an example. Replace them with your own.
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Enter your details and run the calculation.
Alcohol and water volumes are not perfectly additive. This is not a precise OIML calculation, a labelling or excise value, or proof of beverage safety.
Full disclaimerThe calculator uses an approximate formula: water = initial volume × (initial strength / target strength − 1). For 1 US gallon of spirit at 60% and a 40% target you need about 0.5 gallons of water, for an idealized final volume of 1.5 gallons. Alcohol and water contract slightly when mixed and temperature changes the reading, so check the final strength with a measuring instrument. The result is not a labelling or excise value.
Divide the starting strength by the target, subtract 1 and multiply by the volume: 60 / 40 − 1 = 0.5. To 1 US gallon of spirit you add about 0.5 gallons of water and get roughly 1.5 gallons at about 40%. Add the water gradually and measure the strength at the end.
Alcohol and water volumes are not perfectly additive: the mixture contracts, and density depends on temperature. The formula leaves out these corrections, so the result is a guide. It is not a precise official calculation, a labelling or excise value, or proof that a drink is safe.
METHOD
Approximate water = initial volume × (initial ABV / target ABV − 1).
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