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Spirit Dilution Calculator

Calculate water addition to dilute spirits to target proof or ABV. Barrel-proof bottling and proofing calculator for distillers.

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Inputs that matter
Current Proof, Target Proof, Spirit Volume
Output to expect
Spirit Dilution Calculator
  • Check the units and required inputs before comparing results.
  • Keep the assumptions with a copied result so you can reproduce the calculation later.
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Reference & details

How it works

Dilution Formula

Approximate formula accounting for ethanol-water volume contraction (~4%). P in proof (US) or use ABV directly.

Water = (V_start × (P_start/P_target − 1)) ÷ (1 − 0.04)

ABV Dilution

Simplified linear approximation for moderate dilutions. More accurate for small batch craft bottling.

V_water = V_spirit × (ABV_start − ABV_target) ÷ ABV_target

Final Volume

Final volume slightly less than sum due to contraction. Expect 2–4% less volume than arithmetic sum.

V_final = V_spirit + V_water (minus contraction)

Updated: July 2026

Example Scenarios

750 ml at 125 proof diluted to 90 proof requires ~195 ml water. Final volume ~930 ml (contraction adjusted).

100L at 140 proof (70% ABV) to 80 proof (40% ABV): add ~75L water for standard bottling strength.

Cask strength 110 proof — calculate water to hit exactly 100 proof for consistent release across barrels.

FAQ

Depends on starting and target proof. 120 proof to 90 proof on 750ml: approximately 200ml water. Use calculator for exact amount.

Ethanol and water molecules interact, occupying less combined volume. Final volume is 2–4% less than spirit + water arithmetic sum.

Reverse osmosis or deionized water. Avoid chlorinated tap water — chlorine affects flavor. Some distillers use same source water as production.

Add water in stages with rest periods (24–48 hours) for homogenization. Final proof verification after full integration. Oxidation can mellow during resting.

Proof hydrometer or Anton Paar density meter at 20°C. Temperature-correct hydrometer readings. TTB requires accurate proof for tax reporting.

About Spirit Dilution Calculator

Bottling spirits at target proof requires precise water addition calculation. Enter starting volume, current proof, and target proof to calculate water volume needed using the non-linear alcohol dilution formula that accounts for volume contraction.