Calculate how much water to add to whiskey to reach a target ABV or proof, or the strength after adding water, in mL, liters or US fluid ounces.

Estimate a water addition from an ideal additive-volume balance.

US proof is twice ABV. Maximum: 100% ABV or 200 US proof.

Use a target at or below the initial strength. An equal target needs no water.

Display precision
Rounds displayed volumes only.

Whiskey Dilution Formula

The following ideal-volume balance estimates the water to add. Use the same strength basis for BP and DP, and the same volume unit for W and WD. US proof is twice ABV. Real ethanol-water mixtures contract, so this formula is an estimate rather than a precise proofing procedure.

WD = (W × (BP / DP - 1))

Variables:

  • WD is the estimated water to add (US fluid ounces in this example)
  • W is the volume of whiskey (US fluid ounces in this example)
  • BP is the bottle strength in US proof
  • DP is the desired strength in US proof, greater than zero and no higher than BP

How to Calculate Whiskey Dilution?

The following steps outline how to calculate the Whiskey Dilution.

  1. First, determine the volume of whiskey (US fluid ounces).
  2. Next, determine the bottle proof. 
  3. Next, determine the desired proof. 
  4. Next, gather the formula from above = WD = (W * (BP / DP – 1)).
  5. Finally, calculate the Whiskey Dilution.
  6. After inserting the variables and calculating the result, check your answer with the calculator above. 

Example Problem:

Use the following variables as an example problem to test your knowledge.

volume of whiskey (US fluid ounces) = 30

bottle proof = 80

desired proof = 40

WD = 30 × (80 / 40 − 1) = 30 US fluid ounces of water. The ideal final volume is 60 US fluid ounces at 40 US proof (20% ABV), before accounting for contraction or temperature effects.