// CASK STRENGTH DAILY
Proof & Dilution Calculator
US proof is defined in federal regulation as exactly twice the percentage of alcohol by volume (27 CFR § 5.1) , so converting between the two is exact. Estimating a dilution is not: read the note below before trusting the number to the decimal.
ABV ↔ Proof
Exact conversion. Change either field.
Dilution Estimate
How much water it would take to bring a known volume down to a target proof, assuming volumes add up simply when you mix them.
Why this is an estimate, not a measurement
This assumes water and alcohol combine additively by volume , add 100 mL of water to 700 mL of whiskey and get exactly 800 mL. Real ethanol-water mixtures don't quite work that way: they exhibit a well-documented nonideal mixing effect where the actual combined volume comes out very slightly less than the arithmetic sum. In practice that means a real dilution's measured proof will land a little higher than this estimate predicts. Use this to get close, then measure (with a hydrometer, if you have one) and adjust.
Why proof shows up everywhere in bourbon
Most bourbon is bottled between 80 and 100 proof after resting in the barrel at a much higher proof (barrels are legally required to enter aging at no more than 125 proof, and many bourbons leave the barrel well above their bottled strength). Some are bottled at barrel proof / cask strength instead , no water added at all after the barrel. Neither is "better"; they're just different starting points for what you taste. See the glossary for how "proof" itself is used across other bourbon terms, or the guided tasting tool to put a number like this in front of an actual pour.