How to use this calculator
- Enter the current strength of your spirit in %vol (ABV), measured or corrected to 20 °C.
- Enter the volume you have and choose its unit: mL, L, US fl oz or US gal.
- Enter the strength you want to reach and press Calculate.
How the calculation works
Diluting with water does not change the amount of ethanol, so the final volume follows directly from the strengths:
Final volume = Current volume × Current ABV ÷ Target ABVThe water needed is more than final volume − current volume, because an ethanol–water mixture contracts. The calculator works in mass instead: it converts the spirit to mass using its density at 20 °C, finds the mass of water that brings the ethanol mass fraction to the target, and converts that water back to a volume. Densities come from the same reference table the ABV Corrector app uses.
Example
To bring 1 L of spirit at 60 %vol down to 40 %vol, the final volume is 1 × 60 ÷ 40 = 1.5 L. Because of contraction, you need about0.51 L (514 mL) of water rather than 0.5 L.
Accuracy & limitations
- All volumes and strengths are assumed to be at 20 °C.
- Starting strength up to 70 %vol; target strength from 0.5 %vol.
- For pure ethanol–water mixtures. Sugar or other ingredients change density.
- Always confirm the final strength with an alcoholmeter before bottling.
FAQ
Why isn't the water to add simply the final volume minus the starting volume?
When ethanol and water are mixed, the result takes up less volume than the two liquids did separately. To reach the target strength you therefore need slightly more water than the difference between the final and starting volumes. This calculator uses a density table to account for that contraction.
What temperature should the spirit and water be at?
The calculation assumes all liquids and all strengths are at 20 °C. Correct an alcoholmeter reading taken at another temperature with the alcohol temperature correction calculator before using it here.
Should I add all the water at once?
Add most of it, mix, let the spirit rest and return to room temperature, then check the strength with an alcoholmeter and add the remainder in small steps. Mixing releases heat, which temporarily affects readings.
What kind of water should I use?
Distilled, deionised or reverse-osmosis water is normally used, because minerals in tap water can cause cloudiness or off-flavours in spirits.
Why is the maximum starting strength 70 %vol?
The density table behind this calculator covers 0–70 %vol. Rather than extrapolate, the calculator does not return results above that strength.