ABV Calculator
Calculate alcohol by volume from original and final gravity readings for beer, wine or cider.
About the ABV Calculator
Enter the specific gravity you measured before fermentation (OG) and after it finished (FG). The calculator gives the ABV by the standard homebrew formula, a more accurate alternative for stronger brews, and the apparent attenuation.
As yeast turns sugar into alcohol and CO₂, specific gravity falls. The widely used formula multiplies the drop by 131.25. Hydrometer readings should be corrected for temperature.
The formula
ABV ≈ (OG − FG) × 131.25
- OG
- original gravity, before fermentation
- FG
- final gravity, when fermentation is done
Worked example
OG 1.050, FG 1.010
- Drop: 1.050 − 1.010 = 0.040
- ABV = 0.040 × 131.25 = 5.25%
- Alternative formula: 5.34%; apparent attenuation 80%
Questions people ask
Can I use a refractometer?
Yes for original gravity; after fermentation, alcohol skews it, so correct the reading.
What's a typical OG for beer?
About 1.040–1.060 for standard-strength beer.
How do I know fermentation has finished?
The gravity stays the same on two readings a couple of days apart.