What this calculator does
This tool calculates the resulting alcohol percentage (ABV) and the total volume of a drink after you dilute a quantity of liquor with water. In Japan this water-diluted style of serving spirits such as shochu or whisky is called "mizuwari" (literally "water-split"), but the math is universal and applies to any drink you make by mixing a spirit with water, soda, or another zero-alcohol mixer.
How to use it
Enter three values: the volume of liquor you pour (in ml), the alcohol percentage of that liquor (its ABV, where 30 means 30%), and the volume of water you add (in ml). The calculator returns the total drink volume and the final ABV of the mixed drink. Because the same volume unit appears in both the top and bottom of the ratio, you can use any consistent unit and still get the correct percentage.
The formula explained
First, the pure alcohol contained in the liquor is its volume times its strength as a fraction: alcohol = liquorVolume x (liquorAbv / 100). The finished drink's volume is simply liquorVolume + waterVolume (this assumes volumes add directly and ignores the tiny contraction that happens when ethanol and water mix). The final strength is the pure alcohol divided by the total volume, expressed as a percentage: $$\text{ABV} = \frac{\text{Liquor (ml)} \times \dfrac{\text{Liquor ABV (\%)}}{100}}{\text{Liquor (ml)} + \text{Water (ml)}} \times 100$$
Worked example
Pour 50 ml of a 30% shochu and top it with 100 ml of water. Pure alcohol = \(50 \times 30/100 = 15\) ml. Total volume = \(50 + 100 = 150\) ml. Final ABV = \(15 / 150 \times 100 = 10\%\). So you end up with a 150 ml drink at 10% ABV. A stronger pour of 100 ml of 40% whisky with 60 ml water gives 40 ml alcohol in 160 ml, or 25% ABV.
FAQ
Does adding ice count as water? Roughly yes once it melts. Add the approximate melt volume to the water amount for a closer estimate.
Why is my total volume not exactly liquor plus water in real life? Mixing ethanol and water causes a small volume contraction, so the true total is slightly less. This calculator uses the simple additive assumption, which is accurate enough for drinks.
Can I use it for a highball with soda? Yes. Soda water has no alcohol, so treat its volume as the "water added" value.
