Alcohol Dilution Calculator
Enter the starting volume, starting ABV, and a lower target ABV. The calculator applies the standard alcohol-conservation equation to estimate the water to add and ideal final volume in millilitres, litres, US fluid ounces, or US gallons.
Enter the starting volume and ABV.
Choose a lower target strength to estimate the water required.
How Much Water Should You Add?
To reduce an alcohol solution from one ABV to a lower ABV, multiply the starting volume by the starting ABV divided by the target ABV, then subtract the starting volume.
For example, reducing 750 mL at 40% ABV to 30% ABV gives an ideal final volume of 1,000 mL and an estimated water addition of 250 mL.
The answer is an arithmetic planning estimate. Real ethanol-water mixtures can produce a different measured final volume.
Ideal alcohol-dilution examples
These examples use alcohol conservation and ideal volume addition. Measured results can differ.
Swipe horizontally to view the full table.
How to Use the Alcohol Dilution Calculator
Enter the amount of liquid you are starting with and select its volume unit.
Enter the current alcohol by volume and the lower ABV you want to reach.
The calculator immediately shows the estimated water to add, ideal final volume, and alcohol-volume equivalent.
All displayed volumes remain in the selected unit, so no separate conversion is required.
Alcohol Dilution Calculation
The calculation assumes that the amount of alcohol remains unchanged while added water increases the total liquid volume.
Starting volume multiplied by starting ABV is set equal to final volume multiplied by target ABV.
Because both ABV values use the same percentage scale, they can be entered directly as numbers such as 40 and 30.
The alcohol-volume equivalent shown in the result is the starting volume multiplied by ABV divided by 100. It is an arithmetic equivalent, not a physically separated volume of pure ethanol.
Why the Measured Result Can Differ
The calculator assumes that starting liquid volume plus added water equals final liquid volume.
Ethanol-water mixtures do not follow that assumption exactly. Their density and final volume depend on composition and temperature.
For precise proofing, mix thoroughly, allow the liquid and temperature to stabilise, and measure with suitable calibrated equipment or the applicable official procedure.
Commercial and regulated work may require TTB gauging tables, temperature correction, laboratory methods, and production records.
ABV, US Proof, and Reference Temperature
Alcohol by volume expresses ethanol as a percentage of the total liquid volume.
Under U.S. distilled-spirits definitions, proof is twice the percentage of alcohol by volume. A spirit at 40% alcohol by volume is therefore 80 proof.
U.S. regulatory proof is defined at 60°F. Temperature matters because liquid volume and density change as temperature changes.
The calculator accepts ABV rather than proof. Divide U.S. proof by two before entering it.
Hydrometers and Dissolved Solids
A hydrometer estimates strength from liquid density and can be appropriate for suitable ethanol-water mixtures when used correctly.
Sugar, extracts, flavourings, and other dissolved solids can obscure the relationship between density and alcohol content.
TTB proofing guidance uses additional procedures for high-solid spirits, including sample distillation before proof determination.
Do not treat an ordinary hydrometer reading from a sweetened or otherwise complex product as a guaranteed ABV measurement.
Supported Volume Units
The dilution ratio is independent of the selected volume unit because starting volume, water addition, and final volume remain on the same scale.
The implementation also stores each unit's millilitre relationship for consistent reference and converted result values.
US fluid ounces and US gallons are different from Imperial fluid ounces and Imperial gallons.
Volume units supported by the calculator
The calculator distinguishes U.S. liquid units from Imperial units.
Swipe horizontally to view the full table.
When This Calculator Is Not Suitable
Do not use this tool to increase ABV, model distillation, estimate evaporation, or combine two alcoholic liquids of different strengths.
Do not rely on it for liqueurs, extracts, sweetened products, or other mixtures when precise strength depends on density, solids, or a regulated production method.
It is not a substitute for laboratory analysis, licensed production procedures, tax gauging, formula approval, or local labelling requirements.
Handling High-Strength Alcohol
Ethanol is flammable, and higher-strength products can produce ignitable vapour.
Keep alcohol away from flames, sparks, hot surfaces, and other ignition sources. Use suitable containers and follow the manufacturer's safety information.
The calculator determines only an ideal dilution quantity. It does not assess handling conditions, product suitability, or legal compliance.
Privacy and Local Processing
The calculation runs entirely in the browser.
Entered volumes and alcohol percentages are not uploaded, added to a public URL, or permanently stored.
Alcohol Dilution Formulas
The formulas conserve the arithmetic alcohol-volume equivalent and assume ideal volume addition.
Formula variables
- Starting liquid volume
- Starting ABV on a consistent percentage or decimal scale
- Ideal final liquid volume
- Target ABV on the same scale as the starting ABV
- Estimated water addition in the selected volume unit
- Alcohol by volume expressed as a percentage
- U.S. degrees of proof
Examples
Reduce 40% ABV to 30% ABV
1Input
750 mL at 40% ABV with a target of 30% ABV.
Show result
Result
Add an estimated 250 mL of water for an ideal final volume of 1,000 mL.
The measured final volume can differ because ethanol and water are not perfectly volume-additive.
Reduce 50% ABV to 40% ABV
2Input
1 litre at 50% ABV with a target of 40% ABV.
Show result
Result
Add an estimated 0.25 litre of water for an ideal final volume of 1.25 litres.
Reduce 45% ABV to 40% ABV
3Input
700 mL at 45% ABV with a target of 40% ABV.
Show result
Result
Add an estimated 87.5 mL of water for an ideal final volume of 787.5 mL.
Reduce 60% ABV to 40% ABV
4Input
1 US gallon at 60% ABV with a target of 40% ABV.
Show result
Result
Add an estimated 0.5 US gallon of water for an ideal final volume of 1.5 US gallons.
Keep the same ABV
5Input
500 mL at 40% ABV with a target of 40% ABV.
Show result
Result
The estimated water addition is zero and the ideal final volume remains 500 mL.
Frequently Asked Questions
How do I calculate how much water to add to alcohol?
Multiply the starting volume by the starting ABV divided by the target ABV, then subtract the starting volume. This is an ideal arithmetic estimate.
How much water should I add to 750 mL at 40% ABV to reach 30%?
The ideal calculation gives 250 mL of water and a final volume of 1,000 mL.
Can this calculator increase alcohol strength?
No. Adding water can only leave the ABV unchanged or reduce it.
Can the target ABV equal the starting ABV?
Yes. The estimated water addition will be zero.
Can the target ABV be zero?
No. Reaching exactly zero ABV through a finite water addition is not possible, so the calculator requires a target above zero.
How do I convert US proof to ABV?
Divide U.S. proof by two. For example, 80 proof equals 40% alcohol by volume.
What does alcohol-volume equivalent mean?
It is the starting volume multiplied by ABV divided by 100. It represents the arithmetic volume equivalent of alcohol, not a separated physical volume of pure ethanol.
Why might the final measured volume be different?
The formula assumes ideal volume addition. Real ethanol-water mixtures have composition-dependent density and can produce a different final volume.
Can I use a hydrometer when the liquid contains sugar?
Dissolved solids can obscure a simple density-based alcohol reading. A different measurement or laboratory procedure may be required.
Is this suitable for official or regulatory proofing?
No. It is a planning estimate and does not replace calibrated measurement, temperature correction, gauging tables, laboratory analysis, or applicable regulations.
References
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