Daily Figures Edition No Sign-Up • No Tracking • Free Forever Vol. XII — No. 204
plaincalculators.com
Plain Calculators
“The figures, plainly worked — a standing desk of free, no-nonsense calculators.”
Monday, July 20, 2026 Science Price: Free Runs In Your Browser
Find a calculator
Science — Brewing

ABV Calculator

Enter your original and final gravity to get alcohol by volume, apparent attenuation and alcohol by weight.

Filed by The Statistics Desk  |  Method: ABV = (OG − FG) × 131.25
before fermentation
after fermentation
ABV
—
Alcohol by volume, standard formula.
Readout
ABV (alternate formula)—
Apparent attenuation—
Alcohol by weight—
Calories (12 oz)—
Show our math
Enter your figures above to see the step-by-step working.
Everything computed client-sideEverything computed client-side — nothing leaves this page

How the ABV Calculator Works

When yeast ferments a beer, cider or wine, it eats sugar and gives off alcohol and carbon dioxide, so the liquid gets less dense. Measure the specific gravity before fermentation (the original gravity, OG) and after (the final gravity, FG) with a hydrometer, and the drop between them tells you how much alcohol was produced.

The standard homebrew estimate multiplies that drop by 131.25 to get alcohol by volume. This calculator also shows a more refined formula that fits better at higher strengths, the apparent attenuation (what fraction of the sugar the yeast consumed), alcohol by weight, and a rough calorie count per 12 oz. Gravities are typed as specific gravity, for example 1.050 and 1.010.

ABV % = (OG − FG) × 131.25

Frequently Asked Questions

What are OG and FG?

Original gravity (OG) is the specific gravity of your unfermented wort or must; final gravity (FG) is the specific gravity once fermentation finishes. Both are read off a hydrometer or refractometer, typically between about 1.000 and 1.120.

Why are there two ABV formulas?

The simple “× 131.25” formula is accurate for normal-strength beers up to roughly 6–7% ABV. The alternate formula corrects for the fact that the relationship curves at higher gravities, so the two diverge for strong beers and wines.

What is apparent attenuation?

It is the percentage of the original sugar (measured as gravity points) that the yeast fermented out. Most ales land around 70–80%. It is “apparent” because alcohol is lighter than water, which exaggerates the reading slightly.

More From The Desk

Same plain method, different figures