# Alcohol Dilution Calculator

URL: https://speedycalculator.com/calculators/food/alcohol-dilution/
Last updated: 2026-10-30

> The alcohol dilution calculator works out how much water (or a weaker spirit) to add to a strong spirit to reach a target strength – for liqueurs, tinctures, rubbing alcohol or proofing down homemade spirits – and the final volume.

## Inputs

- Strong alcohol strength (ABV) (%)
- Strong alcohol volume (L, ml, US gal, fl oz, cups)
- Water or weak alcohol strength (%)
- Target strength (%)

## Results

- Water / weak alcohol to add
- Final volume (before contraction)
- Contraction (approx.)
- Target strength in US proof

## Formula

```
Water or weak liquid to add = V × (C_strong − C_target) ÷ (C_target − C_weak)
Final volume ≈ V + added volume (minus a little contraction)
```

## Explanation

This is the classic "Pearson square" mixing rule. When alcohol and water mix the volume shrinks slightly (up to about 3–4%), so the final volume is a little smaller and the strength a little higher than the simple calculation – add the water gradually and check with an alcoholmeter.

### How to use the Alcohol Dilution Calculator

- **Strong alcohol strength (ABV)**
- **Strong alcohol volume**
- **Water or weak alcohol strength**
- **Target strength**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Enter the strength and volume of the strong alcohol, the strength of what you are adding (0% for water) and the target strength.

### Tips

- Measure gravity and temperature carefully – hydrometers are calibrated for a specific temperature.
- Keep alcohol calculations conservative: never drink and drive, and know your limits.
- Write down every measurement in a brewing log so you can repeat good batches.
- Chill drinks in an ice-water bath for the fastest, safest cooling.

### Common mistakes to avoid

- Reading a hydrometer at the wrong temperature without correcting it.
- Mixing up ABV (% by volume) and ABW (% by weight).
- Over-priming bottles – too much sugar can make bottles burst.

### Inputs explained

FieldWhat to enterStrong alcohol strength (ABV)In %Strong alcohol volumeUnits: L, ml, US gal, fl oz, cupsWater or weak alcohol strengthIn %Target strengthIn %

### What each result means

- **Final volume (before contraction)** = [Strong alcohol volume] + [Water ÷ weak alcohol to add]
- **Contraction (approx.)** = [Final volume (before contraction)]×0.035×4×([Target strength]÷100)×(1 - [Target strength]÷100)
- **Target strength in US proof** = [Target strength]×2

## Worked example

Inputs — Strong alcohol strength (ABV): 95 %; Strong alcohol volume: 1 L; Water or weak alcohol strength: 0 %; Target strength: 40 %.

Results — **Water / weak alcohol to add = 1.375 L**; Final volume (before contraction) = 2.375 L; Contraction (approx.) = 0.08 L; Target strength in US proof = 80.

## FAQ

**How do I dilute 95% alcohol to 40%?**
Add about 1.375 litres of water to each litre of 95% alcohol.

**Why is the final volume smaller than expected?**
Ethanol and water molecules pack together, so the mixture contracts slightly.

**Can I dilute isopropyl alcohol the same way?**
Yes – e.g. 91% to 70% needs 0.3 L of water per litre.