Calculate alcohol by volume from original and final gravity readings, with attenuation and calories.
The method behind this calculator
Fermentation converts sugar into alcohol, which lowers the density of the liquid. Measuring specific gravity before and after tells you how much sugar was consumed and therefore how much alcohol was produced.
The standard formula multiplies the gravity drop by 131.25, which is accurate for typical beers. The alternate formula corrects better at higher alcohol levels, where the simple version drifts.
How to fill it in
- Take a hydrometer reading before pitching yeast — that is your OG.
- Take a second reading when fermentation finishes — that is your FG.
- Enter both and choose a formula.
The calculation
ABV = (OG − FG) × 131.25
attenuation = (OG − FG) ÷ (OG − 1) × 100%
The default scenario, worked through
The calculator opens with a formula of Standard — (OG − FG) × 131.25. On those figures the ABV is 5.64%. Underneath, Apparent attenuation comes out at 78.2% and Alcohol by weight at 4.49%. Change any field and every figure updates as you type.
Frequently asked questions
What is apparent attenuation?
The percentage of available sugar the yeast consumed. Most ale yeasts land between 70 and 80 percent.
Why do the two formulas differ?
The simple linear formula underestimates at high gravity. The alternate version accounts for the non-linear relationship above roughly 6–7% ABV.
Do I need to correct for temperature?
Yes — hydrometers are calibrated to a specific temperature, usually 20°C. Readings taken warm need adjusting before use.