How much water do you need to add in order to dilute alcohol?

Multiply the original volume by the actual alcohol content and divide that result by the desired alcohol content to get the final volume. Then subtract the original volume from it. For example, if you want to reduce 5 liters of liquid with an alcohol content of 60% vol. to 40% vol., the final volume is 7.5 liters so you need to add 2.5 liters of water.

What is the formula for diluting alcohol?

This formula is based on the law of volume constancy for pure alcohol. The product of initial volume and initial alcohol content equals the product of final volume and final alcohol content (V1 x A1 = V2 x A2). Rearranged, it becomes: The final volume is the initial volume multiplied by the initial alcohol content, divided by the desired final alcohol content.

Is it possible to calculate alcohol content after adding a certain amount of water?

Yes, it is possible. Enter the starting volume and starting alcohol content, set the ending volume to be the sum of the starting volume and the amount of water you plan on adding, and leave the desired ending alcohol content blank. This calculator will then give you the resulting alcohol content.

Why is the actual volume slightly less than what's shown in the calculator?

Because water and alcohol contract slightly when mixed, the actual volume is somewhat less than the sum of the individual volumes. This effect is greatest at about 50% ABV but is small in most alcoholic beverages. If you want to be exact with your fill volume, first adjust for the desired ABV, then add a little water to compensate for the loss.

How do you convert ABV to proof?

In the US, proof is twice the volume percent of alcohol. So a 40% vol would be 80 proof and a 50% vol would be 100 proof. When the Proof option is enabled you can display two alcohol contents simultaneously on the proof scale.

Alcohol Dilution Calculator

Your spirit

Actual alcohol strength

Volume you have now

Target alcohol strength

Final volume (leave blank to calculate)

Water to add

Enter your actual strength, starting volume, and target strength, and this will show the water to add.

Bottling

Plan the bottling run

Work out how many bottles the finished volume fills.

Options

Show US proof equivalents

Convert both alcohol strengths to US proof (proof = 2 x ABV).

Please input values into the fields

The Alcohol Dilution Calculator shows how much water needs to be added to dilute a high-proof alcohol to the desired alcohol content. After measuring the alcohol content of the distillate liquid and selecting the target alcohol content, the tool calculates the amount of water to add as well as the resulting volume. This is a tool used by people who are distilling at home since it is necessary to reduce the alcohol content after taking a high-proof liquid from the still to a drinkable level.

What this calculator can do:

Three of the four fields are filled in and one is left blank. Typically, the actual alcohol content, current volume, and target alcohol content will be entered to determine how much water should be added. It's also possible to work backwards: if a desired final volume is specified and the starting volume is left blank, the tool will show the amounts of liquid and water that need to be mixed together. If the target alcohol content is left blank, the tool will show what the alcohol content would be for a given final volume.

About the calculation equation:

The amount of pure alcohol in the container does not change when water is added; only the total volume changes. The entire calculation is based on this simple principle. If the amount of pure alcohol before and after adding water is the same, then:

V_1 \times A_1 = V_2 \times A_2

Here V1 and A1 stand for the initial volume and alcohol content, respectively, while V2 and A2 stand for the final volume and target alcohol content, respectively. By rearranging the equation to calculate the final volume, we get:

V_2 = V_1 \times \frac{A_1}{A_2}

The amount of water added is the difference between the final volume (V2) and the initial volume (V1). For example: if you have 5 liters of liquid with 60% ABV and want to reduce it to 40% ABV, then you need to add a certain amount of water.

V_2 = 5 \times \frac{60}{40} = 7.5 \text{ L}, \quad \text{water} = 7.5 - 5 = 2.5 \text{ L}

Thus, if you mix 2.5 liters of water with 5 liters of an alcoholic liquid, the end result is a mixture of 7.5 liters with an alcohol content of 40% vol. The 3 liters of pure alcohol contained in the original alcoholic liquid remain at 3 liters even after dilution and are simply distributed over a larger volume of liquid.

The table below shows the calculated values for this example.

Symbol	Meaning	Example
A1	Actual strength before dilution	60 % vol
V1	Volume before dilution	5 L
A2	Target strength after dilution	40 % vol
V2	Volume after dilution	7.5 L
Water	Water added	2.5 L

On volume contraction:

Water and alcohol do not mix completely additively. When mixed together the resulting total volume is slightly less than the sum of the two volumes. This phenomenon is called contraction and it is most pronounced at around 50% ABV. This tool ignores contraction, as do many other desktop tools, to make the numbers easier to understand. For typical liquids the accuracy of the results will be within one percent point. If you need to determine the filled volume exactly then first set the alcohol content to your target value and then add water in small increments while checking with an ABV meter until you have reached the desired volume.

Explanations about "proof", ABV and alcohol content.

The alcohol content (in % vol) gives the proportion of pure ethanol contained in a liquid. In the USA this is double the figure referred to as "proof". So 40% vol is equivalent to 80 proof and 50% vol is 100 proof. If the option "Proof" is enabled, you can display two alcohol contents simultaneously on the scale of the "proof" value. To measure the alcohol content at home, immerse an alcoholometer in the sample. The reading may vary with temperature, so most alcoholometers are calibrated to a reference temperature of 20 degrees Celsius. Make sure that the liquid has cooled down to this temperature or correct the reading beforehand before using the result.

Tips for reducing alcohol content:

Add water gradually and not all at once. Let the mixture sit for a while to settle before checking the alcohol content with an alcoholometer. Use clean, low-mineral-content water to avoid cloudiness or changes in taste. Many distillers let liquids that have just had their alcohol content adjusted sit for a few days. This is because the flavor can change slightly even after dilution. Remember to use the same units throughout the process and you can switch between liters, gallons, and milliliters for each volume.

This tool is for general reference only. In many regions, home distillation of spirits is regulated or restricted. Please research your local laws. Be sure to discard the first run and drink responsibly.

Frequently asked questions

How much water do you need to add in order to dilute alcohol?: Multiply the original volume by the actual alcohol content and divide that result by the desired alcohol content to get the final volume. Then subtract the original volume from it. For example, if you want to reduce 5 liters of liquid with an alcohol content of 60% vol. to 40% vol., the final volume is 7.5 liters so you need to add 2.5 liters of water.
What is the formula for diluting alcohol?: This formula is based on the law of volume constancy for pure alcohol. The product of initial volume and initial alcohol content equals the product of final volume and final alcohol content (V1 x A1 = V2 x A2). Rearranged, it becomes: The final volume is the initial volume multiplied by the initial alcohol content, divided by the desired final alcohol content.
Is it possible to calculate alcohol content after adding a certain amount of water?: Yes, it is possible. Enter the starting volume and starting alcohol content, set the ending volume to be the sum of the starting volume and the amount of water you plan on adding, and leave the desired ending alcohol content blank. This calculator will then give you the resulting alcohol content.
Why is the actual volume slightly less than what's shown in the calculator?: Because water and alcohol contract slightly when mixed, the actual volume is somewhat less than the sum of the individual volumes. This effect is greatest at about 50% ABV but is small in most alcoholic beverages. If you want to be exact with your fill volume, first adjust for the desired ABV, then add a little water to compensate for the loss.
How do you convert ABV to proof?: In the US, proof is twice the volume percent of alcohol. So a 40% vol would be 80 proof and a 50% vol would be 100 proof. When the Proof option is enabled you can display two alcohol contents simultaneously on the proof scale.

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Disclaimer: This calculator is provided for general informational and educational purposes only. Our calculators are under active development, and results may be inaccurate, incomplete, or unsuitable for your situation. Always verify the figures independently and seek advice from a qualified professional before relying on them. We make no warranties and accept no liability for any loss or decision arising from use of this tool.

References

Distilling Spirits: Alcohol Dilution Calculator
Reference dilution tool for home distillers.
NIST/OIML: Alcoholometry and ethanol-water mixtures
Background on alcohol strength measurement and volume contraction.