ABV Calculator
Enter your original and final gravity to get alcohol by volume and apparent attenuation. Both readings can be temperature-corrected here if you took them warm or cold.
Results
- Apparent attenuation
- 80%
- Original gravity (OG)
- 1.05
- Final gravity (FG)
- 1.01
Gravity drop: 40 points
How ABV is calculated
ABV = (OG - FG) × 131.25. Yeast converts dissolved sugars into alcohol: a beer dropping from 1.050 to 1.010 sheds 40 gravity points and lands near 5.25% ABV. Apparent attenuation is the share of extract consumed - typical ale yeast attenuates 65-80%, and drier styles sit higher.
Garbage in, alcohol out: make the inputs trustworthy with the hydrometer temperature correction, or convert refractometer samples first with the Brix to SG calculator.
Frequently asked questions
Why does the formula multiply by 131.25?
The constant compresses two physical steps into one: it converts the gravity drop into alcohol by weight using the density relationship between ethanol and water, then converts alcohol by weight to alcohol by volume. It is the standard homebrewing approximation and is accurate to within a few hundredths of a percent across typical beer gravities.
Can I use a refractometer for the final gravity?
Not directly. Once alcohol is present, a refractometer reads several Brix points too high, so the plain sugar-to-SG conversion no longer applies. Either use a hydrometer for the final reading, or run the refractometer value through an alcohol correction formula first - then enter both gravities here.
What is apparent versus real attenuation?
Apparent attenuation - what this calculator shows - compares gravities as measured, but alcohol is lighter than water, so it overstates how much sugar was actually consumed. Real attenuation is roughly 80% of the apparent number. Brewers compare apparent attenuation against their yeast strain specs, typically 65-80% for ale yeasts.
My FG is higher than the recipe says - what now?
First confirm the reading is temperature-corrected and taken after two stable samples a day apart. Common causes of a genuinely high FG: unfermentable crystal or Cara malts, mashing too warm for the yeast, an underpitched or stressed yeast, or a stalled fermentation. If gravity is unchanged for several days, rouse the yeast or warm it a few degrees before assuming it is finished.