Diluting 65% spirit to 40% ABV: a worked batch example

Multiply the starting volume by ABV expressed as a decimal: 83 L × 0.65 = 53.95 litres of absolute alcohol (LAA). Adding water does not add alcohol. For this calculation we assume no alcohol is lost through handling or evaporation.

LAA provides a useful check: the same alcohol quantity should appear on both sides of the calculation, with all volumes and strengths on a consistent temperature basis.

Divide the alcohol volume by the target strength: 53.95 ÷ 0.40 = 134.875 L. This is the final solution volume associated with that alcohol quantity at 40% ABV. It is not an instruction to add 134.875 L of water.

Subtract the starting spirit volume: 134.875 − 83 = 51.875 L. The same result comes from 83 × (65 ÷ 40 − 1). Keep the extra decimal places during calculation, but do not confuse displayed precision with measurement accuracy.

For another batch size, 65% to 40% gives an estimated water-to-spirit ratio of 0.625 to 1. A 20 L starting batch therefore has a 12.5 L water estimate. A 100 L starting batch has a 62.5 L estimate.

Alcohol and water contract when mixed. Consequently, subtracting starting spirit volume from target final volume does not give an exact water requirement. Use the estimate to plan the work, then confirm the result using measured strength, temperature and the appropriate proofing procedure.

Record actual additions separately from the initial estimate. If the batch has not reached the target, calculate the next adjustment from the newly measured volume and ABV, rather than repeatedly using the original figures.

At the theoretical 134.875 L volume, 750 mL bottles give 134.875 ÷ 0.75 = 179.833… bottles: 179 whole bottles with 625 mL remaining, before losses. This is a planning ceiling under the stated assumptions, not a promised packaged yield.

Use the actual finished volume and account for transfer, filtration and packaging losses before costing saleable bottles. The bottle yield calculator helps check whole-bottle counts. The Costing & Proofing Toolkit brings proofing estimates, batch costs, bottle economics and production records into one Excel workbook.

Open the dilution calculator and enter your measured starting volume, starting ABV and target ABV. Keep the output beside your batch record, then replace estimated quantities with verified measurements as production progresses.