How much water should I add to whisky?
Choose a target, then calculate
A target ABV is useful if you want to compare pours at roughly the same strength. It does not tell you which pour will taste best. Start with the volume of whisky actually in the glass and the ABV on its label.
For a 30 mL pour at 60% going to 50%: 30 × (60 ÷ 50 − 1) = 6 mL of water. Going to 40%: 30 × (60 ÷ 40 − 1) = 15 mL. Both are additive-volume estimates, without correction for contraction.
Examples for a 50 mL pour
| Starting ABV | Target ABV | Water estimate |
|---|---|---|
| 46% | 40% | 7.5 mL |
| 50% | 40% | 12.5 mL |
| 60% | 45% | 16.7 mL |
| 60% | 40% | 25 mL |
The 16.7 mL entry is rounded from 16.666… mL. Small pours amplify measuring errors, so use a marked measure if repeatability matters.
Why “a few drops” has no single ABV answer
The effect of water depends on the pour size, starting strength and volume added. Drops are not a standardized volume across droppers. A fixed addition also changes a small pour more than a large one.
If your goal is taste, add a small measured amount, stir and taste before adding more. Keep notes if you want to repeat the result. You do not need to reach 40% simply because it appears in a reference table.
What if I already added water?
Estimate the new ABV with starting volume × starting ABV ÷ (starting volume + added water). For 50 mL at 60% with 10 mL of water, the estimate is 50 × 60 ÷ 60 = 50% ABV. This also assumes additive volumes.
Ice makes a repeatable target harder because its meltwater changes over time. A fixed-water calculation does not predict how quickly ice will melt.
From tasting glass to batch
The same ratio works at larger scale, but production needs more careful measurement. Use the Stillbench dilution calculator with consistent units. For batch work, verify final strength and temperature rather than scaling a tasting-glass estimate and treating it as exact.
If you also need batch costing, bottle economics and production records, explore the Stillbench Costing & Proofing Toolkit. The free calculator is enough for a quick individual dilution estimate.