# Alcohol Dilution Calculator

Calculate how much water to add to dilute spirits or high-proof alcohol to your target ABV. Works for distilling, homebrew, and cocktail prep.

## What this calculates

Whether you are cutting down a barrel-strength bourbon, proofing a fresh distillate, or diluting high-proof spirits for cocktail use, this calculator tells you exactly how much water to add to reach your target ABV.

## Inputs

- **Current ABV** (%) — min 1, max 100 — Current alcohol percentage by volume
- **Target ABV** (%) — min 0.5, max 99 — Desired alcohol percentage by volume
- **Current Volume** (mL) — min 1, max 1000000

## Outputs

- **Water to Add** — Volume of water needed to reach target ABV
- **Final Volume** — Total volume after dilution
- **Pure Alcohol Volume** — Volume of pure ethanol in the mixture
- **Proof (before)** — US proof of the original spirit
- **Proof (after)** — US proof of the diluted spirit

## Details

Here's how dilution works:

**Final Volume = (Current ABV / Target ABV) x Current Volume**
**Water to Add = Final Volume - Current Volume**

This is based on the standard dilution equation (C1 x V1 = C2 x V2), where the amount of pure alcohol stays constant and only the total volume changes.

**Example:** You have 750 mL of 60% ABV (120 proof) spirit and want to dilute it to 40% ABV (80 proof):
- Final volume = (60 / 40) x 750 = 1,125 mL
- Water to add = 1,125 - 750 = 375 mL

**Important notes for distillers:**

- **Use distilled or filtered water.** Tap water with chlorine or high mineral content can cause cloudiness (louching) and off flavors.
- **Add water slowly.** Pour the water into the spirit, not the other way around, and add it gradually over several minutes. Rapid dilution can cause haze.
- **Temperature matters.** The standard reference temperature for measuring proof is 60F (15.6C). Alcohol/water mixtures are slightly non-ideal, meaning the final volume may be 2-3% less than the simple calculation predicts due to molecular contraction. For precise proofing, measure ABV with a hydrometer after dilution at the reference temperature.
- **Let it rest.** After dilution, let the mixture sit for at least 24-48 hours before final proof measurement. The alcohol and water need time to fully integrate.

For home cocktail use, this level of precision is not necessary. The calculator gives you a close-enough answer for practical purposes.

## Frequently Asked Questions

**Q: Why is my final volume less than expected after diluting?**

A: When ethanol and water mix, the molecules pack together more tightly than either liquid alone. This is called volume contraction. A mixture of 500 mL alcohol and 500 mL water produces about 970 mL of solution, not 1,000 mL. The effect is most pronounced around 50-60% ABV. For casual dilution this difference is negligible, but commercial distillers measure the actual ABV after mixing rather than relying purely on the calculation.

**Q: What is the difference between ABV and proof?**

A: In the United States, proof is simply double the ABV. So 40% ABV = 80 proof, and 50% ABV = 100 proof. The UK historically used a different proof system based on the gunpowder test, where 100 UK proof was about 57.15% ABV. Most countries outside the US now use ABV exclusively. This calculator shows both for convenience.

**Q: Can I dilute any spirit this way?**

A: Yes, the math works for any spirit: whiskey, vodka, rum, gin, moonshine, or any other distilled alcohol. However, some spirits (especially those with essential oils like absinthe or ouzo) will turn cloudy when diluted below certain ABV thresholds because the oils become less soluble at lower alcohol concentrations. This is normal and expected for those spirits.

**Q: How do I measure ABV at home?**

A: Use an alcoholometer (a hydrometer calibrated for alcohol/water mixtures). Float it in a sample of your spirit at the reference temperature (60F/15.6C) and read the ABV scale. Make sure the sample has no residual sugar, as sugar affects the density reading. For sugar-containing liqueurs, you would need a more advanced method like distillation and measurement of the distillate.

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Source: https://vastcalc.com/calculators/health/alcohol-dilution
Category: Health & Fitness
Last updated: 2026-04-08