Alcohol Dilution Calculator

Alcohol and water contract slightly on mixing, so the final volume is a percent short.

Water to add500 mLtaking 1,000 mL from 60% to 40%

Alcohol by volume5.25%from 1.05 down to 1.01

Apparent attenuation80%in the normal range for an ale yeast

Gravity points fermented40

Above 8 percent the factor driftsnot an issue here131.25 is fitted to ordinary worts

Final volume1,500 mLin theory — alcohol and water contract slightly on mixing, so expect a per cent less

Pure alcohol present600 mLunchanged by dilution, which is the whole point

Attenuation is more diagnostic than ABV. Most ale yeasts reach 70 to 80 per cent; well below that means the fermentation stalled or the mash ran hot, and well above it suggests something is eating sugars the brewer's yeast cannot.

The formula

ABV = (OG - FG) * 131.25 ; attenuation = (OG - FG) / (OG - 1)

Sugar in, alcohol out

Original gravity measures the sugar dissolved before fermentation and final gravity what is left after. The drop between them is what the yeast ate, and multiplying by 131.25 converts it to alcohol by volume. That factor is empirical, fitted to typical beer worts, and it drifts high above about 8 % — strong brews need one of the more elaborate formulas.

Attenuation tells you what happened

The percentage of sugar the yeast actually consumed is more diagnostic than the ABV. Most ale yeasts manage 70 to 80 %. Well below that and the fermentation stalled, or the wort was full of unfermentable sugars from a high mash temperature. Well above and you may have a wild yeast eating things the brewer's yeast cannot.

Diluting is C1V1 = C2V2

Cutting a spirit to strength is the same arithmetic as any other dilution, with alcohol as the solute. One caution the arithmetic does not capture: alcohol and water contract slightly on mixing, so the final volume is a per cent or two less than the sum of the parts. It matters when bottling to a line.

Recipes are starting points

Ovens run hot or cold by 20 degrees, flour absorbs water differently by season and brand, and the same joint of meat cooks at a different rate depending on its shape rather than its weight. Everything here is a planning figure that gets you close enough to start, and the thermometer, the scales and your own notes from last time are what finish the job.