ABV Calculator
Take the gravity drop and multiply by 131.25.
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 — this page is the quick standalone version for brew day.
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.
How do you calculate ABV from OG and FG?
ABV ≈ (OG − FG) × 131.25. A beer that drops from 1.052 to 1.012 is about 5.25% ABV. The constant 131.25 converts the specific-gravity drop into percent alcohol by volume.
Why is the constant 131.25?
It comes from the relationship between the sugar fermented and the ethanol produced. 131.25 is the standard multiplier that turns a gravity drop into ABV for normal-strength beer; you'll also see 131 or 132 used.
Is the simple ABV formula accurate?
For beers under about 1.080 OG it's accurate to within roughly 0.1% ABV. Above that the gravity-to-alcohol relationship curves, so big beers like imperial stouts and barleywines read slightly low; formulas such as Cutaia's are more accurate there.
What's the difference between ABV and ABW?
ABV is alcohol by volume; ABW is alcohol by weight. Because ethanol is less dense than water, ABW ≈ ABV × 0.79. Homebrew and commercial labels use ABV.
Do I need to temperature-correct my gravity first?
Yes, if your sample isn't at the hydrometer's calibration temperature. Correct the reading first with the hydrometer correction calculator, then use the corrected OG and FG here.