How much water do I add to my spirit?
The three numbers you need
Measure the volume of spirit you have, its starting alcohol by volume (ABV), and the strength you want to reach. Use the same volume unit throughout. Enter 60 and 40 for the ABV percentages, or 0.60 and 0.40; do not mix the two formats.
The target must be above zero and below the starting strength. Water can reduce ABV; it cannot raise it. If both strengths are equal, no water is needed.
The spirit dilution formula
Estimated water = V × (A ÷ T − 1), where V is the starting spirit volume, A is the starting ABV, and T is the target ABV.
The corresponding target final volume is V × A ÷ T. For example, 1 L × 60 ÷ 40 = 1.5 L. Subtracting the original 1 L gives an estimated water addition of 0.5 L. This subtraction assumes additive volumes; actual alcohol–water mixtures do not behave exactly that way.
Water-addition reference table
These calculated estimates start with 1 litre of spirit. They ignore contraction and assume comparable measurement temperatures.
| Starting ABV | Target ABV | Water estimate |
|---|---|---|
| 50% | 40% | 250 mL |
| 60% | 40% | 500 mL |
| 65% | 40% | 625 mL |
| 70% | 40% | 750 mL |
| 95% | 40% | 1,375 mL |
Scale the estimate by your starting volume. A 10 L batch at 65% ABV has an estimated water addition of 6.25 L to approach 40% ABV.
Use the result at the bench
Use the free spirit dilution calculator to check your arithmetic. For a production batch, record starting volume, measured strength, measurement temperature, planned addition and actual additions. Approach the target in controlled stages, mix thoroughly, allow temperature to stabilize, and measure again using an appropriate calibrated instrument.
There is no universal extra-water percentage that corrects every batch for contraction. Use suitable alcoholometric tables or validated measurement procedures when precision matters. The calculator and the Toolkit both provide planning estimates, not contraction-corrected production certification.
Common questions
Does the formula work in gallons?
Yes. If the starting volume is in US gallons, the estimated water is in US gallons. Do not mix US and Imperial gallons.
Is proof the same as ABV?
US proof is twice the ABV percentage. You may use US proof for both strengths in the ratio, but do not combine a proof value with an ABV value.
Can I use this for a sweetened liqueur?
This is a spirit-and-water planning model. Sugar and other dissolved ingredients complicate volume and density measurements; use a method appropriate to the finished product.