Home Brewing ABV Calculator
Calculate the alcohol content of your homebrew beer. Enter original gravity and final gravity readings.
Specific gravity before fermentation
Specific gravity after fermentation
How is beer alcohol content (ABV) calculated?
ABV is calculated using the difference between original gravity (OG) and final gravity (FG): ABV = (OG - FG) × 131. This standard formula estimates alcohol by volume based on the sugar consumed by yeast during fermentation. For example, OG 1.050 to FG 1.012 = (1.050 - 1.012) × 131 = 4.98% ABV.
What is a good original gravity for homebrew?
OG depends on your target ABV: Session beers: 1.030-1.045, Standard ales: 1.045-1.060, Strong ales: 1.060-1.080, Barleywines: 1.080-1.120+. Higher OG requires more yeast and careful fermentation management. Always pitch enough yeast for your gravity - under-pitching causes off-flavors.
Why should I measure FG?
Final gravity tells you if fermentation is complete. A stable FG near your target means fermentation finished. If FG is higher than expected, fermentation may be stuck (under-attenuation). Common causes: incomplete fermentation, high alcohol inhibition, temperature issues, or insufficient yeast. Let it rest 2-3 weeks before bottling to ensure stability.
What if my FG is higher than expected?
If FG is higher than calculated, your beer may be under-fermented. Causes: yeast stress (temp extremes), insufficient yeast, poor nutrients, or high alcohol inhibition. Solutions: rouse yeast by swirling, warm to 68-72°F, add fresh yeast (re-pitch), or accept the lower ABV. Check gravity over 3 days - if stable, fermentation is likely complete.