Spirit Dilution Calculator
Work out exactly how much water to add to bring a home-distilled spirit down to your target strength — using a real mass-balance calculation, not the volume-additive shortcut most online calculators still use.
Bar shows the original spirit and the added water proportional to their volume in the final mixture.
Before you dilute
- Pour the spirit into the water, not the other way around — the usual practical technique for a clean, even result.
- Dilute in one step, directly in the container you'll store it in, rather than adding water gradually across several separate steps.
- Measure and dilute near room temperature (about 20°C) — hydrometer/alcoholmeter readings are calibrated at that temperature, and a reading taken well above or below it can be off by a noticeable margin.
- This tool covers dilution only — bringing an already-finished spirit down to strength. Safe distillation technique itself (separating heads and tails, methanol/fusel-oil awareness) is a separate topic this calculator doesn't cover.
How this is calculated
The final volume you'll end up with is exact: it follows directly from the fact that the amount of pure ethanol in your spirit doesn't change when you add water — only the volume it's dissolved in does. Where most online dilution calculators go wrong is the very next step: they assume the water needed is simply the difference between that final volume and your starting volume, which silently assumes water and ethanol mix by adding their volumes together. They don't — mixing ethanol and water measurably shrinks the total volume below the sum of the parts, because of how the molecules interact. This tool instead works out the water needed from mass (which really is additive, unlike volume), using real measured density data for ethanol-water mixtures at each strength — which is why the answer here is usually a few percent different from, and more accurate than, the simpler formula.
Common questions
Why is this more accurate than most dilution calculators I can find online?
Because most of them use a formula that assumes mixing ethanol and water is volume-additive — pour in X liters of water, get exactly X liters more total volume. That's not how it works: the mixture actually contracts, so that shortcut understates how much water you need, sometimes by several percent, not just a rounding error. This calculator works from mass instead, using real ethanol-water density data, which gets the water amount right.
Why can't I dilute to a target strength higher than my starting strength?
Because adding water can only lower the alcohol content, never raise it — diluting is a one-way street. If you need a stronger spirit, that has to come from distillation itself, not from this calculator.
Does this cover everything I need to know about making spirit safely?
No — this tool is scoped specifically to diluting an already-finished spirit to drinking strength. It doesn't cover distillation technique itself, including safely separating the early ("heads") and late ("tails") fractions of a run, which is where health-relevant concerns like methanol and fusel oils actually need to be managed. If you're new to distilling, that's a separate topic to learn properly before you start.
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