Calculate how much water to add to reduce alcohol concentration. Perfect for diluting spirits, proofing down whiskey, and adjusting cocktail strength.
Diluting spirits and high-proof alcohol is a precise process used by distillers, bartenders, and homebrewers. When you need to reduce a 60% ABV barrel-strength whiskey to the standard 40% bottling proof, you can't just eyeball the water addition — you need the exact volume calculated with the dilution equation. The tricky part is that alcohol and water mix non-linearly: blending equal volumes of water and pure ethanol produces less total volume than the sum of the two, thanks to molecular contraction.
The basic dilution formula is C₁V₁ = C₂V₂, where C is concentration and V is volume. Starting concentration × starting volume = desired concentration × final volume. From this, the amount of water to add is: Water = V₁ × (C₁/C₂ − 1). For most practical purposes (spirits under 80% ABV), this formula is accurate within ±0.5%.
This calculator handles spirit proofing, cocktail dilution, and homebrew adjustment. It works with both ABV percentage and US proof, and calculates the resulting volume, water amount, temperature adjustment, and the flavor impact of different dilution levels. It's essential for anyone bottling spirits, adjusting barrel-proof whiskey, or creating consistent cocktails.
Precise dilution prevents wasting expensive spirits and ensures consistent bottle strength. Essential for distillers proofing down batches and bartenders creating balanced cocktails. Keep these notes focused on your operational context. Tie the context to the calculator’s intended domain. Use this clarification to avoid ambiguous interpretation. Align this note with review checkpoints. Apply this where interpretation shifts by use case.
Water to add = Volume × ((Current ABV / Target ABV) − 1). Final Volume = Volume × (Current ABV / Target ABV). US Proof = ABV × 2. Note: This assumes ideal mixing. Real mixing with ethanol contraction reduces final volume ~3-4% at high concentrations.
Result: Add 375 mL water for 1125 mL at 40% ABV
Water = 750 × (60/40 − 1) = 750 × 0.5 = 375 mL. Final volume = 750 + 375 = 1,125 mL. The 750 mL of 60% spirit becomes 1,125 mL of 40% spirit.
Professional distillers follow a precise proofing protocol. After distillation, the spirit comes off the still at a high proof (typically 130-170 proof / 65-85% ABV). It's then diluted to barrel entry proof (typically 125 proof / 62.5% ABV for bourbon) and aged. After aging, the final proofing down to bottling strength (usually 80-100 proof / 40-50% ABV) requires careful calculation and slow water addition to prevent hazing.
When ethanol and water molecules combine, the ethanol molecules fit into the spaces between water molecule clusters, causing the total volume to decrease. This "excess volume of mixing" is maximized around 50% ethanol by volume, where the contraction can be up to 3.7%. For practical purposes at typical spirit proofing levels (40-60% ABV), the contraction is 1-3%. Most calculators (including this one) use the ideal mixing formula, which is accurate enough for home use.
Professional bartending relies on understanding dilution. A stirred cocktail gains about 25-30% water from the ice during stirring. A shaken cocktail gains about 30-40%. This predictable dilution is factored into recipes. A Martini mixed 2:1 gin to vermouth is designed to be about 25% ABV in the glass after dilution. If you reduce the stirring time, the drink is stronger but also less integrated.
Use the formula: Water = Volume × ((Current ABV / Target ABV) − 1). For 750 mL at 60% ABV to 40%: 750 × (60/40 − 1) = 375 mL of water. Use distilled or mineral water for best results.
Yes — use distilled, reverse osmosis, or quality mineral water. Tap water with chlorine or heavy minerals can affect flavor. Room temperature water blends more smoothly than cold water.
US proof is simply ABV × 2. So 40% ABV = 80 proof. UK proof uses a different historical scale, where 100° UK proof ≈ 57.15% ABV.
Ethanol and water molecules pack together more tightly than either liquid alone, causing molecular contraction. A mix of 500 mL ethanol + 500 mL water = about 960 mL, not 1000 mL. This effect is strongest around 50-60% ABV.
Add water to spirit slowly, stirring gently. Adding spirit to water can cause "shocking" which creates a temporary haze (louche effect). For small quantities it doesn't matter much.
Let diluted spirits rest at least 24 hours before tasting or bottling. The molecular integration takes time, and freshly diluted spirit often tastes harsh or disjointed compared to rested spirit.