Brewing ABV Calculator
Compare two widely used fermentation ABV estimates and calculate apparent attenuation and US proof equivalent.
Use two stable gravity readings
Original gravity is measured before fermentation. Final gravity should be measured after fermentation has stopped and the reading is stable.
Temperature-correct the reading when required by the hydrometer calibration. Refractometer readings after fermentation need a separate alcohol correction.
Why two ABV estimates are shown
The simple equation multiplies the gravity drop by 131.25 and works as a practical brewing estimate. The alternate equation models the relationship differently and can diverge as strength rises.
Neither is a laboratory determination. The difference between them is useful uncertainty context rather than an error to hide.
Examples
Typical ale
Input
OG 1.050; FG 1.010
Show result
Result
About 5.25% ABV and 80% apparent attenuation
Frequently Asked Questions
Can I use Brix readings directly?
No. This interface expects specific gravity. Refractometer readings after alcohol is present require a correction model.
Is US proof double ABV?
Yes. TTB explains that proof is calculated as twice the percentage alcohol by volume.
References
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