🍺 ABV Calculator
Enter your original and final gravity to see your beer's alcohol by volume and how far the yeast attenuated — the two numbers every brewer checks at the end of fermentation.
🍺 Calculate Your ABV
What is an ABV Calculator?
It turns two hydrometer readings into the number that defines your finished beer. Take an original gravity (OG) before fermentation and a final gravity (FG) after, and the calculator estimates alcohol by volume along with apparent attenuation — how completely the yeast ate through the wort's sugars.
Use it to confirm a batch hit its target strength, to compare yeast performance, or to troubleshoot a fermentation that finished higher or lower than expected. The ABV figure uses the widely-used (OG − FG) × 131.25 estimate, so treat it as a reliable guide rather than a lab-exact value.
❓ Frequently Asked Questions
How does the ABV calculator work?
Enter your original gravity (OG), measured before pitching yeast, and your final gravity (FG), measured once fermentation finishes. The tool applies the standard homebrew formula ABV = (OG − FG) × 131.25 to estimate alcohol by volume, and calculates apparent attenuation as (OG − FG) ÷ (OG − 1) × 100 so you can see what percentage of the sugars the yeast consumed.
What is apparent attenuation?
Apparent attenuation is the proportion of fermentable sugars the yeast converted, read straight off your hydrometer. It's called 'apparent' because alcohol is lighter than water, so it drags the reading below the true sugar content. Most ale yeasts attenuate 70–80%; a lower figure can mean an under-attenuated, sweeter beer, while a very high figure points to a drier finish.
Why is the 131.25 factor an estimate?
The (OG − FG) × 131.25 formula is a linear approximation that works well for typical beer strengths but drifts at very high gravities, where a slightly higher factor (up to ~135) is more accurate. For everyday brewing it's close enough; for strong beers or competition, use an alternative alcohol-corrected formula or a lab measurement.
Should I temperature-correct my gravity readings first?
Yes. Hydrometers are calibrated to a specific temperature (often 20°C/68°F), so a hot sample reads low and a cold one reads high. Either cool your sample to the calibration temperature or apply a temperature correction before entering OG and FG, otherwise your ABV and attenuation will be off.