Gauging Calculator

Alcohol expands as it warms, so a hydrometer reading taken at any temperature other than the standard reference point of 60°F reads a proof that doesn't match the spirit's true strength. This calculator applies a simplified linear correction -- approximately 0.4 proof degrees per degree Fahrenheit away from 60°F -- to translate an Observed Proof reading at Spirit Temperature back to Corrected Proof at 60°F, the reference condition proof and ABV are conventionally reported at. Corrected ABV is simply Corrected Proof divided by 2, following the standard US definition where proof is always exactly twice the alcohol-by-volume percentage. Proof Correction is the raw adjustment amount itself -- positive when the spirit was measured warmer than 60°F (since warm alcohol reads higher than its true strength) and negative when measured colder.

Proof Gallons per Wine Gallon expresses the corrected proof as a fraction of 100, the unit conversion used in US federal alcohol volume and tax reporting, where a wine gallon at 100 proof equals exactly one proof gallon. Correction Factor restates the same temperature adjustment as a multiplicative ratio -- Corrected Proof divided by Observed Proof -- instead of an absolute proof-degree offset, which is handy if you need to scale a related quantity (like a proof-gallon total) by the same proportion the temperature correction changes proof, rather than adding a flat number of degrees to it. Observed Proof is what this calculator responds to most directly, since it enters the corrected result with a coefficient of 1, while Spirit Temperature's effect runs through the smaller 0.4-per-degree correction factor. What it does not account for: the real relationship between temperature, proof, and true alcohol content is nonlinear and varies by proof level -- the official TTB (Alcohol and Tobacco Tax and Trade Bureau) gauging tables used for federal reporting and tax purposes are built from precise alcohol-water density tables, not a single linear rate, so this simplified approximation is for estimation and planning only, not for regulatory or tax-reporting purposes.