What is the Mizuwari Dilution Calculator?
Mizuwari (literally "water-cut") is the Japanese custom of diluting a strong spirit such as whisky or shochu with cold water for an easier-drinking glass. This calculator tells you exactly how much water to add to a given amount of liquor so that the finished drink reaches the alcohol strength you want, and how much total volume you will end up with. Although it is framed around mizuwari, the math is universal dilution by conservation of alcohol and works for any spirit, anywhere.
How to use it
Enter three numbers: the amount of liquor you have in millilitres, the alcohol content of that liquor as a percentage (ABV), and the target alcohol content you want the finished drink to have. The calculator returns the amount of water to add and the total volume of the resulting mizuwari. The target strength must be greater than zero and no higher than the liquor's own strength, because adding water can only weaken a drink, never strengthen it.
The formula explained
The pure alcohol in the glass does not change when you add water. The amount of alcohol is volume times strength, so liquor volume times liquor ABV must equal the final volume times the target ABV. Rearranging gives the total volume as liquor volume times (liquor ABV / target ABV). The water to add is simply that total minus the liquor you started with.
$$\text{Water to Add} = \text{Liquor (ml)} \times \left( \frac{\text{Liquor ABV}}{\text{Target ABV}} - 1 \right)$$
The percentages enter only as a ratio, so it does not matter whether you treat them as percents or fractions. This model assumes volumes add up exactly; in reality ethanol and water contract a little when mixed, but the difference is small and unimportant for a casual drink.
Worked example
You have 50 ml of 30% ABV whisky and want a 12% mizuwari. Total volume = \(50 \times (30 / 12) = 50 \times 2.5 = 125\) ml. Water to add = \(125 - 50 = 75\) ml. So pour 75 ml of water into your 50 ml of whisky to get 125 ml of drink at 12% ABV.
FAQ
Why can't the target be higher than the liquor? Adding water only dilutes, so you cannot reach a higher percentage than the spirit already has. If you ask for a higher strength the calculator warns you.
Is the result exact? It assumes volumes are additive. Real alcohol-water mixtures shrink by a few percent, so the actual volume may be marginally less, but for serving a drink this is negligible.
Does this work for shochu or other spirits? Yes. The calculation is pure dilution math and applies to any liquor of any strength, measured in any consistent units.
