Alcohol Dilution Calculator
Calculate how much water to add to bring a spirit down to a target strength.
Last updated · View algorithm, constants and default inputs (JSON)
About this calculator
Estimate a water addition from the conservation of pure alcohol. The calculation treats volumes as additive; ethanol and water can contract when mixed, so measure the finished strength and volume rather than treating this as an exact bottling recipe.
Worked example
calculated with the default values below
Starting volume 750 ml · Current strength 50 % · Target strength 40 % Water to add 187.5 ml · Final volume 937.5 ml · Final volume 0.938 L · Dilution ratio 1.250 x
General background references
Disclaimer
These calculators give general cooking guidance. Ingredient density, oven calibration, altitude and equipment all vary, and safe minimum internal temperatures always take precedence over timings. Follow the food-safety advice issued by your national authority.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
water = V × ABV₁ ÷ ABV₂ − V
- water
- water to add (ml)
- V
- initial volume (ml)
- ABV₁
- current strength (%)
- ABV₂
- target strength (%)
Assumes additive volumes, although ethanol and water can contract when mixed. Target strength must be below current strength; verify the finished mixture with a suitable alcohol measurement.
Frequently asked questions
Why does reducing 50% ABV to 40% add one-quarter of the starting volume?
The tool assumes alcohol volume is conserved and volumes add directly. Final volume is starting volume × current ABV ÷ target ABV: 750 ml at 50% becomes 937.5 ml at 40%, so the displayed water addition is 187.5 ml, one-quarter of the starting volume. Real ethanol–water mixtures can contract, which this simple calculation does not model.