Understanding your dilution result
The table shows example dilutions computed with C1V1 = C2V2 for a 750 ml starting volume. Real mixtures contract slightly, so the measured ABV after mixing runs marginally off the simple-arithmetic target.
| Starting ABV | Target ABV | Water to add (per 750 ml) | Final volume |
|---|---|---|---|
| 60% | 40% | 375 ml | 1125 ml |
| 63.5% | 46% | 285.3 ml | 1035.3 ml |
| 95% | 40% | 1031.3 ml | 1781.3 ml |
| 50% | 43% | 122.1 ml | 872.1 ml |
- Ethanol-water mixing causes slight volume contraction (the mixture occupies less volume than the sum of its parts), so C1V1 = C2V2 results are close approximations; precise work uses density measurement and official alcoholometric tables (e.g. OIML R 22) instead.
- Add water gradually and mix gently; rapid dilution of whisky can cause haze as flavor oils come out of solution at lower ABV.
- Distilled or demineralized water is the conventional choice for dilution, since minerals in hard water can affect clarity and flavor.
- This calculator only lowers strength — the target ABV must be below the current ABV. Raising strength is a blending calculation with a second, stronger spirit.
What is alcohol dilution?
Alcohol dilution is the addition of water to a spirit to lower its alcohol by volume (ABV) — the percentage of the liquid's volume that is pure ethanol. Distillers routinely dilute high-proof new-make spirit or cask-strength whisky down to bottling strength, and home enthusiasts dilute cask-strength bottles or neutral spirit for liqueurs and tinctures. The arithmetic follows the standard dilution equation C1V1 = C2V2: the amount of pure alcohol stays constant while the total volume grows.
The dilution equation treats volumes as perfectly additive, but ethanol and water are not: when mixed, the combined volume is slightly smaller than the sum of the parts — a well-documented physical effect called volume contraction. Because of this, simple C1V1 = C2V2 results land very close to, but not exactly on, the target ABV. Commercial producers verify final strength by density measurement against official alcoholometric tables rather than by volume arithmetic alone.
Water quality matters for flavor and clarity. Distilled or demineralized water is the usual choice for diluting spirits, because mineral-rich hard water can cause haze or dull flavors. Whisky is also best diluted slowly and gently, since rapid dilution can push flavor oils out of solution and cloud the spirit.
How to use this alcohol dilution calculator
- Enter the starting volume of your spirit in milliliters.
- Enter the current ABV — for example 60% for a cask-strength whisky.
- Enter the target ABV you want to reach; it must be lower than the current ABV.
- Read the water to add, the resulting final volume and the pure alcohol content, then verify the real strength with a hydrometer if precision matters.
The formula behind dilution: C1V1 = C2V2
The dilution equation states that concentration times volume is constant when only solvent is added: C1V1 = C2V2. Solving for the final volume gives V2 = V1 × C1 ÷ C2, and the water to add is the difference V2 − V1. The pure alcohol content is V1 × C1 ÷ 100 and does not change during dilution.
Worked example: 750 ml of spirit at 60% ABV diluted to 40% ABV. Final volume = 750 × 60 ÷ 40 = 1125 ml, so you add 1125 − 750 = 375 ml of water. The pure alcohol is 750 × 60 ÷ 100 = 450 ml throughout.
Common mistakes
- Computing the water as a simple percentage of the starting volume — the correct amount comes from V2 = V1 × C1 ÷ C2, which grows steeply as the target ABV drops.
- Expecting the measured ABV to match the arithmetic exactly — ethanol-water volume contraction shifts real mixtures slightly, so verify with a hydrometer for precise work.
- Confusing ABV with proof — US proof is exactly twice the ABV (80 proof = 40% ABV), so mixing up the units doubles or halves the calculation.
- Using hard tap water — dissolved minerals can cause haze and off-flavors; distilled or demineralized water is the convention.
- Adding all the water at once to a cask-strength whisky — slow, staged dilution reduces the chance of cloudiness.
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How much water do I add to dilute 60% ABV to 40%?
For 750 ml at 60% ABV, the final volume at 40% is 750 × 60 ÷ 40 = 1125 ml, so you add 375 ml of water — half the original volume. The 450 ml of pure alcohol stays constant; only the total volume changes. Verify with a hydrometer if the exact strength matters, since ethanol-water mixing contracts slightly.
What is the C1V1 = C2V2 dilution equation?
C1V1 = C2V2 states that concentration multiplied by volume stays constant when you add only solvent: the pure alcohol before dilution (C1 × V1) equals the pure alcohol after (C2 × V2). Rearranged, the final volume is V2 = V1 × C1 ÷ C2 and the water to add is V2 − V1. It is the standard first approximation for diluting any solution.
Why is the result only approximate for alcohol?
Ethanol and water molecules pack together more tightly than either liquid alone, so a mixture occupies slightly less volume than the sum of its parts — a documented effect called volume contraction, strongest in mid-range mixtures. Simple volume arithmetic therefore lands close to but not exactly on the target ABV. Distillers measure final strength by density using official alcoholometric tables.
What water should I use to dilute spirits?
Distilled or demineralized water is the conventional choice, because minerals in hard tap water can create haze and dull flavors. Add the water gradually and mix gently — diluting whisky quickly from cask strength can push flavor oils out of solution and cloud the spirit.
What is the difference between ABV and proof?
ABV (alcohol by volume) is the percentage of the liquid's volume that is pure ethanol. In the United States, proof is defined as exactly twice the ABV, so a 40% ABV spirit is 80 proof. Always enter ABV percentages in this calculator, not proof values.
Can this calculator increase the ABV of a spirit?
No. Adding water can only lower alcohol concentration, so the target ABV must be below the current ABV. Raising strength would require adding higher-proof spirit, which is a blending calculation with two alcohol sources rather than a simple dilution.
Kaynaklar
- OIML R 22. International Alcoholometric Tables — density/strength relationships for ethanol-water mixtures. International Organization of Legal Metrology (1975).
- US Alcohol and Tobacco Tax and Trade Bureau (TTB). Distilled Spirits — proof and gauging references. ttb.gov.
- CRC Handbook of Chemistry and Physics — density of ethanol-water mixtures (volume change on mixing).