ABV Calculator

Determine alcohol by volume from original and final gravity readings. Supports multiple measurement scales including SG, Plato, and Brix. Shows apparent and real attenuation percentages alongside calorie estimates per serving.

Calculator
Presets:

Gravity Readings

Results

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ABV %
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ABW %
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Attenuation %
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Cal / 12 oz

How to Use

  1. 1
    Measure your original gravity

    Take a hydrometer or refractometer reading before pitching your yeast. Record this as your original gravity (OG). A typical ale might read 1.050, meaning the wort is 5.0% denser than water due to dissolved sugars.

  2. 2
    Measure your final gravity

    After fermentation completes and the beer has stabilized — typically 1-2 weeks for most ales — take another gravity reading. This final gravity (FG) reflects the remaining unfermentable sugars after yeast have consumed the fermentable portion.

  3. 3
    Calculate and verify your result

    The calculator uses the standard formula: ABV = (OG - FG) × 131.25, or the more precise Balling equation for higher-gravity beers. Cross-check against TTB tables if you are brewing commercially, as regulatory reporting requires accurate ABV measurement.

About

Alcohol by volume (ABV) is the fundamental measurement of alcoholic strength in beer, expressing the percentage of pure ethanol in a finished beverage by volume. For brewers, accurately calculating ABV is essential for recipe development, style compliance, responsible consumption communication, and regulatory reporting.

The brewing process converts fermentable sugars into ethanol and carbon dioxide through yeast metabolism. The amount of alcohol produced is directly proportional to the difference between the original gravity (OG) of the wort before fermentation and the final gravity (FG) of the finished beer. Hydrometers measure the density of liquid relative to water, and since dissolved sugars increase density while ethanol decreases it, the gravity drop during fermentation provides a reliable proxy for alcohol content.

Modern brewing science offers several equations of varying accuracy, from the simplified standard homebrewing formula to the precise Balling equation used in professional breweries. The choice of formula matters most at the extremes — for session beers under 5% ABV, any standard formula yields adequate results, while barleywines and imperial stouts above 10% ABV benefit from more sophisticated calculations. Understanding the principles behind ABV measurement helps brewers produce more consistent results and communicate accurately about their creations.

FAQ

How accurate is the homebrewing ABV formula?
The standard formula (OG - FG) × 131.25 is accurate within approximately 0.3% ABV for beers below 8% ABV. For higher-gravity beers, the formula slightly underestimates alcohol because the relationship between gravity and alcohol is not perfectly linear at higher sugar concentrations. The more precise Balling or Calver equations improve accuracy for strong ales and barleywines. For commercial TTB compliance purposes, a certified laboratory analysis using gas chromatography provides the most legally defensible measurement.
Can I use a refractometer for final gravity readings?
Refractometers are highly accurate for original gravity but require a correction factor for final gravity readings because dissolved alcohol refracts light differently than sugar solutions. Using a raw refractometer reading for FG without applying the Sean Terrill correction formula will give you a falsely high gravity reading, leading to an underestimate of actual ABV. Most brewing calculators include a refractometer correction tool — input your OG refractometer reading and FG refractometer reading to obtain the corrected FG before calculating ABV.
What factors affect ABV accuracy in homebrewing?
Hydrometer calibration is the most common source of error — standard hydrometers are calibrated at 60°F (15.6°C), and readings taken at different temperatures require a correction. Yeast strain and fermentation completeness significantly affect FG; under-attenuated beer will show a falsely high FG and therefore underestimate ABV. CO2 dissolved in beer can cause hydrometer samples to appear lighter than they actually are, so degassing your sample before reading improves accuracy. Finally, refractometer readings on fermented beer require the alcohol correction mentioned above.
What is the difference between ABV and ABW?
ABV (Alcohol By Volume) expresses the volume of pure ethanol as a percentage of total liquid volume and is the standard measurement used in most countries for beer labeling. ABW (Alcohol By Weight) expresses the weight of ethanol as a percentage of total liquid weight. Because ethanol is less dense than water, ABW is always lower than ABV by approximately 20% — a 5% ABV beer is roughly 4% ABW. The TTB in the United States allows beer labels to use either measurement, though ABV is far more common. To convert, ABW = ABV × 0.789.
Why does my calculated ABV differ from commercial examples?
Commercial breweries use certified laboratory methods including gas chromatography and ebulliometry to measure ABV with regulatory precision. These methods account for variables that gravity-based calculations cannot capture, such as residual CO2, non-ethanol volatiles, and complex sugar interactions. Additionally, most commercial breweries measure ABV after packaging, accounting for any conditioning or refermentation. For homebrewing purposes, gravity-based calculations are entirely sufficient for recipe development and personal knowledge, but should not be used for any commercial labeling or regulatory compliance without proper laboratory verification.