Water to Add: 80% → 40% ABV
Standard volume method. Verify the final strength with a hydrometer before bottling.
Per 1 Litre
1000mL water
Per 750 mL bottle
750mL water
Per 1 US gallon
3785mL water
Final volume / litre
2000mL
water to add = volume × (current ABV − target ABV) ÷ target ABV
= 1000 × (80 − 40) ÷ 40 = 1000 mL per litre
Open the interactive ABV Dilution Calculator →
= 1000 × (80 − 40) ÷ 40 = 1000 mL per litre
About this dilution
80% approaches the azeotropic limit reached only by efficient reflux columns, while 40% is the legal minimum and standard bottling strength for most spirits. Bringing 80% down to 40% means adding roughly 1000 mL of water for every litre of spirit, increasing the batch to about 2000 mL.
For casual reduction the standard volume method above is accurate enough. When bottling at an exact legal strength, switch to OIML Precise mode in the calculator, which corrects for the slight volume contraction that occurs when ethanol and water mix.
Verify before bottling: a calibrated alcoholmeter is the only way to confirm you have hit 40% ABV. Measure at 20°C.
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Common questions
How much water do I add to dilute 80% ABV to 40%?
Add roughly 1000 mL of water to each litre of 80% spirit to reach 40% ABV. The formula is water to add = volume times (current ABV minus target ABV) divided by target ABV.
Why should I verify the result with a hydrometer?
Ethanol and water contract slightly when mixed, so the real strength can sit just under the calculated figure. Always confirm with a calibrated alcoholmeter at 20°C before bottling.
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