Calculate the Alcohol By Volume (ABV) of your homebrew based on gravity readings.
Last updated: March 2026
Example: 1.050 for a standard ale
Example: 1.010 after fermentation
Alcohol by Volume (ABV) is a standard measure of how much alcohol (ethanol) is contained in a given volume of an alcoholic beverage. It is expressed as a volume percentage of the total liquid. ABV is the global standard for labeling spirits, wines, and beers, making it essential for regulatory compliance and consumer understanding.
In brewing, we measure the density of the liquid (Specific Gravity) before and after fermentation. Since alcohol is less dense than water, the drop in gravity tells us exactly how much sugar was converted into alcohol by the yeast. This relationship between gravity and alcohol content is so reliable that gravity readings are the gold standard for ABV prediction in professional brewing.
Why This Matters: ABV directly affects flavor, mouthfeel, and fermentation time. A 5% ale drinks very differently from a 12% barleywine, not just because it has less alcohol, but because yeast behaves differently at higher alcohol levels.
How Gravity Works: Water has a gravity of 1.000. Sugar solutions are denser, so 1.050 means 5% heavier than water. As yeast consumes sugars, gravity drops. The gravity drop indicates how much fermentable sugar was consumed—provided fermentation completed and no other factors (like temperature shifts or stuck fermentation) interfered.
The standard formula is accurate up to ~7% ABV. Use the high-gravity formula for beers over 10% ABV to account for ethanol's physiological effect on yeast.
Let's calculate the ABV for a typical IPA:
Step 1: Subtract Final from Original
1.065 - 1.012 = 0.053
Step 2: Multiply by Conversion Factor
0.053 × 131.25 = 6.956
Step 3: Round to 2 Decimal Places
6.956 approx 6.96 percent ABV
Final Answer: This IPA is approximately 6.96 percent ABV
The standard formula (OG - FG) × 131.25 is highly accurate for beers up to 6-7% ABV. For high-gravity beers (Imperial Stouts, Barleywines over 10% ABV), consider the alternate formula: ABV = (76.08 × (OG-FG)) / (1.775-OG) × (FG/0.794), which accounts for ethanol's inhibition of yeast fermentation at high concentrations.
Apparent Attenuation is the percentage of fermentable sugars that yeast converted into alcohol and CO2. Formula: (OG - FG) / (OG - 1.0) × 100. Most ale yeasts attenuate 70-80%, while lagers typically attenuate 65-75%. Low attenuation (<60%) suggests incomplete fermentation; high attenuation (>85%) indicates vigorous yeast activity and may produce a dry beer.
Hydrometers are calibrated to a specific temperature (usually 15°C or 20°C). If your wort is warmer, it's less dense, giving a false low reading. If cooler, it reads false high. A 10-degree temperature difference can shift ABV by 0.3-0.5%. Always use a temperature correction chart or calculator to adjust readings to the calibration temperature.
Not directly — alcohol distorts refractometer readings, typically making FG appear 0.5-1.0 higher than actual. However, you can estimate FG using a correction formula based on both OG (hydrometer) and FG (refractometer), or simply use a hydrometer for both OG and FG measurements to maintain consistency.
ABV (Alcohol by Volume) measures alcohol as a percentage of the total liquid volume, while ABW (Alcohol by Weight) measures it as a percentage of total weight. Most brewers use ABV because it's the standard reported on labels; ABW is typically about 20% lower numerically since alcohol is less dense than water.
Different yeast strains have varying attenuation rates—the ability to ferment sugars into alcohol—typically ranging from 60% to 80%. Using the attenuation rate specific to your strain predicts your final FG, which then feeds into the ABV formula. Compare predicted vs. actual ABV to refine future recipes.
Yes: Divide the gravity difference by 7.5 for a rough estimate. Example: (1.065 - 1.012) ÷ 7.5 ≈ 7%. This is about 0.15% off from the standard formula and works well for beers under 10% ABV. For high-gravity beers, always use the standard formula for accuracy.
A stuck fermentation means yeast has stopped converting sugars. Check gravity readings 3 days apart to confirm; if they plateau, rehydrate yeast or pitch a fresh starter. Once fermentation restarts, recalculate using updated readings to determine your revised final ABV.
Take gravity readings 3 days apart; if they remain unchanged, fermentation is done. Your actual ABV will then match the calculator's prediction based on starting and final gravities. Most brewers also confirm by tasting—the beer should taste dry with no residual sweetness.
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