Alcohol Dilution Calculator
How much water to add to bring a spirit down to the strength you want — and what volume you end up with.
Diluting works on the amount of pure alcohol, which does not change when you add water: starting volume × starting ABV = final volume × target ABV.
How the alcohol dilution calculator works
Diluting works on the amount of pure alcohol, which does not change when you add water: starting volume × starting ABV = final volume × target ABV. Rearranged, the final volume is the starting volume multiplied by the ratio of the strengths, and the water to add is the difference.
One real-world wrinkle: alcohol and water contract slightly when mixed, so the finished volume is a fraction under the arithmetic — around 2–3% at spirit strengths. For home use the difference is negligible; for anything sold by volume it is not.
Formula: final volume = start volume × (start ABV ÷ target ABV); water = final − start
Worked examples
| Inputs | Water to add | Note |
|---|---|---|
| 700 ml at 60% down to 40% | 350 ml | add 350 ml — 1,050 ml finished |
| Cask strength 58% to 46% | 130 ml | add 130 ml |
| 96% neutral spirit to 40% | 1,400 ml | add 1,400 ml |
FAQFrequently asked questions
How much water do I add to dilute a spirit?
Enough to bring the volume up to start volume × start ABV ÷ target ABV. Going from 700 ml at 60% to 40% means adding 350 ml.
Why does the alcohol amount stay the same?
Because water adds volume, not alcohol. The percentage falls purely because the total grew.
What is contraction?
Alcohol and water pack together more tightly than they do apart, so the mixture is a few per cent smaller than the sum. It matters for bottling, not for a drink.
Should I use distilled water?
For cask-strength whisky, many prefer soft or distilled water so minerals do not affect the taste. For mixing, tap water is fine.
Can I dilute with something other than water?
Yes, but the arithmetic changes if the other liquid contains alcohol — this page assumes the addition is alcohol-free.
Where these figures come from
- US FDA — Safe Minimum Internal Temperatures — the internal temperatures the roasting calculator targets
- NIST SP 811 — Guide for the Use of the International System of Units — the exact weight and volume conversions used throughout
- US Food and Drug Administration — food safety and labelling standards
Last checked: September 2026. Baking ratios follow standard baker's percentage practice; roasting guidance follows published safe internal temperatures.