ABV Calculator
How strong is your beer?
ABV (alcohol by volume) tells you how strong your beer is. A session pale ale might be 4.5%. A barleywine pushes 10%+. It comes down to one thing: how much sugar your yeast ate.
You measure gravity before fermentation (OG) and after (FG). The bigger the drop, the more sugar your yeast converted to alcohol. In the recipe builder, ABV updates automatically as you adjust your grain bill and yeast selection, but this standalone version is handy on brew day.
ABV
from OG / FGEnter your original and final gravity readings to estimate alcohol by volume.
If your sample temperature differs from your hydrometer's calibration temperature, correct the reading first with the hydrometer correction calculator.
How We Calculate It
The industry standard formula. Accurate to within 0.1% ABV for beers under 1.080 OG.
That's it. The gravity drop times 131.25. It works because the relationship between sugar consumed and alcohol produced is nearly linear for normal-strength beers.
A beer with OG 1.052 and FG 1.012:
(1.052 − 1.012) × 131.25 = 0.040 × 131.25 = 5.25% ABV
For high-gravity beers
Above about 1.080 OG, the linear relationship between gravity drop and alcohol starts to curve. More accurate alternatives exist (like the Cutaia formula), but for the vast majority of beers the simple formula is within a tenth of a percent. We use the standard approach because the difference only shows up in imperial stouts and barleywines, and even then it's small.
Where This Comes From
The 131.25 constant comes from the well-established relationship between gravity drop and ethanol production in fermentation chemistry. It simplifies a more complex calculation into something practical, and it holds remarkably well for the beers most of us are brewing.
See all the numbers come together in real time.
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