Alcohol Dilution Calculator
Find how much water to add to lower alcohol percentage to a target ABV, and see the final volume.
This calculator runs entirely in your browser. Nothing you enter is uploaded or stored.
Note: This is an educational estimate. Real-world mixing of alcohol and water can shrink slightly in total volume (volume contraction), and a hydrometer reading is the only sure way to confirm strength. Use this tool for planning, not for legal labeling or commercial sale claims.
How to use this tool
Enter the current volume of your spirit and pick its unit. Type the current ABV (alcohol by volume percentage) shown on the bottle, then enter the target ABV you want to reach. Press Calculate dilution. The tool returns the water blend volume you should add, the final total volume after mixing, and the matching US proof. You can only lower a percentage by adding water, so the target ABV must be smaller than the current ABV.
The formula: C1V1 = C2V2
V2 = (C1 x V1) / C2
water to add = V2 - V1
C1 = current ABV, V1 = current volume
C2 = target ABV, V2 = final volume
The amount of pure alcohol does not change when you add water, so the alcohol in the starting liquid (C1 x V1) equals the alcohol in the finished liquid (C2 x V2). Rearranging gives the final volume V2. Subtracting the starting volume from the final volume tells you how much water to blend in. US proof is simply twice the ABV, so a proof adjustment falls out of the same math.
A real example
Say you have 750 mL of a spirit at 40% ABV and you want to bring it down to 20% ABV. Using C1V1 = C2V2: V2 = (40 x 750) / 20 = 30000 / 20 = 1500 mL. So the final volume is 1500 mL, and the water to add is 1500 - 750 = 750 mL. In other words, adding 750 mL of water doubles the volume and halves the strength, taking it from 80 proof down to 40 proof.
Common questions
What is the alcohol dilution calculator formula?
It uses the dilution rule C1V1 = C2V2, where C is concentration (ABV) and V is volume. Because the pure alcohol amount stays constant when you add water, the final volume is (current ABV x current volume) divided by target ABV. The water to add is the final volume minus the current volume.
Can I raise the ABV with this tool?
No. Adding water can only lower alcohol percentage, never raise it. If your target ABV is equal to or higher than your current ABV, the tool will ask you for a lower target. Increasing strength would require adding more alcohol, which this calculator does not cover.
Why is my real final strength a little off?
When alcohol and water mix, the combined liquid takes up slightly less space than the two parts added separately. This volume contraction is small but real, so the final ABV measured with a hydrometer can be a touch different from the theoretical number. For exact results, dilute in steps and measure as you go.
How does proof relate to ABV?
In the United States, proof is exactly twice the ABV. A spirit at 40% ABV is 80 proof, and at 20% ABV it is 40 proof. This tool shows the proof adjustment alongside the ABV so you can read either number, whichever your recipe or label uses.
Does the unit I choose change the answer?
The water to add is calculated in whatever volume unit you select, since the ratio is the same in milliliters, liters, ounces, or gallons. Pick the unit that matches your measuring tools so you do not have to convert by hand. The final volume is reported in the same unit.