ABV Calculator
Enter your original gravity (OG) and final gravity (FG) from your hydrometer readings to get alcohol by volume, apparent attenuation, and an estimated calorie count.
Results
Formula used: –
Attenuation = (OG − FG) ÷ (OG − 1) × 100. Calories are estimated from real extract and alcohol by weight — close enough for planning, not lab-accurate.
How the ABV formula works
When yeast ferments sugar into alcohol and CO₂, the beer's density drops. The standard homebrew formula converts that drop into alcohol percentage: ABV = (OG − FG) × 131.25. It is simple and accurate enough for most beers under ~6% ABV.
The alternate formula — ABV = (76.08 × (OG−FG) ÷ (1.775 − OG)) × (FG ÷ 0.794) — corrects for the fact that alcohol is less dense than water, which the simple formula ignores. The two agree within a tenth of a point on a 5% pale ale but diverge on big beers, so use the alternate for barleywines and imperial stouts.
Frequently asked questions
How do you calculate ABV from OG and FG?
The standard homebrew formula is ABV% = (OG − FG) × 131.25. For stronger beers above ~6% ABV, the alternate formula shown above is more accurate.
What is a good attenuation for beer?
Most ales land at 70–80% apparent attenuation. Below ~65% can mean a stuck fermentation; above ~85% can mean a very dry beer or contamination. See how to read a hydrometer if your numbers look off.
How many calories are in a 12 oz beer?
A typical 5% ABV 12 oz beer has roughly 150–170 calories from alcohol plus residual carbs. Stronger, sweeter beers run higher.