Free homebrew ABV calculator. Enter original gravity and final gravity to get alcohol by volume, ABW, apparent attenuation and calories per serving.
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Take a hydrometer reading before fermentation starts (original gravity) and another after it finishes (final gravity), then enter both above. The calculator applies the standard homebrewing formula, ABV = (OG - FG) × 131.25, and also reports alcohol by weight, apparent attenuation and an estimated calorie count for your serving size. These are hobby estimates based on your readings, not laboratory measurements.
Yeast turns sugar into alcohol and carbon dioxide. Sugar makes the liquid denser and alcohol makes it lighter, so the drop in density between the start and the end of fermentation measures how much sugar became alcohol. The standard hobby formula is ABV = (OG - FG) × 131.25.
Worked example: a beer that starts at 1.050 and finishes at 1.010 has a gravity drop of 0.040, so (1.050 - 1.010) × 131.25 = 5.25% ABV. For strong brews above about 8% ABV, a longer nonlinear formula that accounts for the density of alcohol gives a slightly higher and more realistic figure, but for typical beers, wines, ciders and meads the simple formula is close enough.
Sanitize a trial jar and fill it with a sample, never dip the hydrometer into the fermenter. Lower the hydrometer in, give it a gentle spin to shake off clinging bubbles, and read the scale at eye level where the flat surface of the liquid meets the stem, not the meniscus climbing the glass.
Take the original gravity reading after the wort or must is mixed and cooled but before you pitch the yeast, and take the final gravity reading only after the gravity has been stable for two days in a row. Write both readings down with the date, and pour the sample away rather than back into the fermenter to keep infection risk low.
Original gravity (OG) is the density of the liquid before fermentation, measured against pure water at 1.000. It tells you how much dissolved sugar is available for the yeast, so a higher OG means a stronger potential drink: session beers often start around 1.040, standard ales around 1.050 to 1.060, and meads and dessert wines can start above 1.100.
Final gravity (FG) is the density after fermentation, showing how much sugar the yeast left behind. Most beers finish between 1.008 and 1.015, while dry wines and meads can finish below 1.000 because alcohol is lighter than water. The difference between the two readings is the only number the ABV formula needs.
ABV (alcohol by volume) measures alcohol as a percentage of the drink's volume, the number printed on almost every label. ABW (alcohol by weight) measures it as a percentage of the drink's weight. Because ethanol is less dense than water, about 0.79 grams per milliliter, the same drink always has a lower ABW than ABV.
The conversion is simple: ABW = ABV × 0.793, so a 5.25% ABV beer is about 4.17% ABW. Homebrewers almost always talk in ABV; ABW shows up mainly in older brewing literature and some tax contexts.
Apparent attenuation = (OG - FG) / (OG - 1) × 100. It is the share of the available extract the yeast fermented, and it tells you what to expect in the glass.
Below 65%: very sweet, thick, possibly a stalled fermentation. 65 to 72%: sweet and full-bodied. 72 to 80%: balanced, the middle for pale ales, lagers and amber ales. 80 to 85%: dry, light body, clean finish. Above 85%: very dry and thin, compare against your yeast strain's published range. Wine and mead yeasts routinely push past 95% and can even exceed 100% apparent attenuation, which is normal because alcohol weighs less than water. If your number is far below the yeast maker's range, suspect underpitching, cold fermentation or a misread hydrometer before you blame the recipe.
Hydrometers are calibrated at a stated temperature, usually 60F (15.5C) or 68F (20C). A sample read warmer than that reads a little low and a sample read colder reads a little high, so cool the sample close to the calibration point or add the correction from your hydrometer's correction table.
Refractometers need only a few drops and are handy before fermentation, but alcohol skews their reading once fermentation has started, so post-fermentation refractometer readings need a dedicated correction. When in doubt, trust a hydrometer for the final gravity reading.
Beer calories come from two places: the alcohol, about 7 calories per gram, and the residual sugar and other extract left in the finished drink. This calculator combines both from your gravity readings, then scales the result to your serving size, defaulting to a 12 oz (355 ml) serving.
The result is a planning estimate: a 5.25% ABV beer works out near 141 kcal per 12 oz, while sweeter or stronger brews climb quickly. Actual calories vary with recipe, carbonation and measurement, so treat the number as a guide for labeling and logging, not a nutrition-facts panel.
ABV (alcohol by volume) is the percentage of a drink's volume that is pure alcohol. For homebrew you measure the original gravity (OG) before fermentation and the final gravity (FG) after, then apply ABV = (OG - FG) × 131.25. The gravity drop shows how much sugar the yeast turned into alcohol.
Original gravity is the density of the wort or must before fermentation, taken after mixing but before pitching the yeast. Final gravity is the density after fermentation is complete. OG tells you the potential strength; FG tells you how much sugar is left. The difference between them drives the ABV calculation.
Apparent attenuation is the percentage of the available sugars the yeast fermented, calculated as (OG - FG) / (OG - 1) × 100. It tells you how dry or sweet the finished drink will be and whether fermentation ran its full course.
Most beer yeasts achieve 65 to 85% apparent attenuation. Below 65% usually means a sweet beer or a stalled fermentation; 72 to 80% is the balanced middle for ales and lagers; above 85% drinks very dry. Wine and mead yeasts routinely exceed 95%.
ABV measures alcohol as a percentage of volume, ABW as a percentage of weight. Because ethanol is less dense than water, ABW is always lower for the same drink: ABW = ABV × 0.793. ABV is the figure used on nearly all labels.
From the alcohol content (about 7 calories per gram) plus the residual sugars and extract left after fermentation. This calculator combines both from your OG and FG readings and scales the total to your serving size. It is an estimate, not a lab measurement.
Yes. Hydrometers are calibrated at a stated temperature, usually 60F or 68F. A warmer sample reads low and a colder sample reads high, so cool the sample near the calibration temperature or apply a temperature correction before trusting the reading.
Not reliably. The gravity-based formula needs both readings. Without an OG you can only make a rough guess from the recipe, the amount of fermentable sugar used, or a laboratory alcohol analysis.
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