Beer ABV Calculator

This tool uses the common homebrew estimate ABV = (OG - FG) x 131.25, where OG and FG are your specific gravity readings. For example, 1.050 minus 1.010 is 0.040, and 0.040 x 131.25 gives 5.25 percent.

Apparent attenuation is the share of available sugar the yeast fermented, calculated as (OG - FG) / (OG - 1) x 100. Most ales finish between about 70 and 80 percent, so an OG of 1.050 dropping to 1.010 gives 80 percent.

Alcohol is lighter than water, so a hydrometer in finished beer reads lower than the true sugar content would suggest. That inflates the figure slightly, which is why it is labelled apparent attenuation rather than real attenuation.

No. The calorie number is a rough rule of thumb, computed as ABV x 2.5 x 12 for a 12 oz serving and rounded to a whole number. Real calories also depend on residual sugars and the grain bill, so treat it as a ballpark.

Each reading must be a plausible specific gravity between 0.9 and 1.2, and the final gravity cannot be higher than the original gravity. Values outside that range or in the wrong order are rejected with an error.

Fermentation lowers gravity as sugar turns to alcohol, so FG should be less than or equal to OG. If you entered an FG larger than your OG, swap the two readings or recheck which one you measured.

Yes. Hydrometers are calibrated to a specific temperature, usually around 20 C, so a warm sample reads low. Apply your hydrometer's temperature correction before entering the value for a more accurate ABV.

Some brewers use an alternate equation that curves upward for high-gravity beers. The 131.25 factor here is the simple linear version, which is accurate for typical beers and only drifts slightly for very strong brews above about 8 percent.

Yes. The calculation runs entirely in your browser, so your gravity readings never leave your device and nothing is stored.