ABV Calculator

ABV, alcohol by volume, is calculated from two hydrometer or refractometer readings: original gravity (OG), taken before fermentation, and final gravity (FG), taken once fermentation has finished. OG measures the density of the unfermented wort, must, or juice; a typical beer OG runs 1.030 to 1.120, while wine musts run higher, 1.070 to 1.130. FG measures the sugar and dissolved solids left behind after yeast consumes the fermentable sugar, and it is always lower than OG when fermentation succeeds. A final reading equal to or close to the original points to a stuck fermentation rather than a measurement error.

Two formulas convert the gravity drop into ABV. The standard formula, ABV = (OG - FG) x 131.25, is a linear approximation that suits most beers. The alternate formula, from Daniels, is ABV = (76.08 x (OG - FG) / (1.775 - OG)) x (FG / 0.794); it accounts for the nonlinear relationship between gravity and alcohol at higher ABV values and is the more accurate choice above 6% ABV. Apparent attenuation, a separate figure, equals ((OG - FG) / (OG - 1)) x 100 and reports the percentage of available sugar the yeast actually consumed. A low attenuation value points to weak yeast health, poor pitch rate, or fermentation temperature stress.

Settings holds the choice between the standard and alternate formulas and a step-by-step view that substitutes the entered gravity readings into the chosen equation and shows each intermediate result.

A beer reads 1.050 original gravity and 1.010 final gravity, a drop of 0.040. The standard formula gives 0.040 x 131.25 = 5.25% ABV. Apparent attenuation is (0.040 / 0.050) x 100 = 80%, meaning the yeast consumed 80% of the available sugar.

Determining alcohol content from gravity readings supports recipe development, quality control, and regulatory compliance across homebrewing and winemaking.

• Homebrewing: Track the ABV of each batch to refine recipes over time. Comparing OG and FG readings across batches reveals yeast performance trends and fermentation consistency.
• Winemaking: Measure the alcohol yield from grape must or fruit juice. The expected attenuation indicates whether a wine will finish dry, off-dry, or sweet.
• Cider and Mead Production: Calculate ABV for apple cider, perry, or honey-based mead. Periodic gravity readings compared against the original measurement track fermentation progress.
• Recipe Development: Estimate the expected ABV before brewing day from a target OG and a projected FG based on yeast attenuation data. Grain bills or sugar additions can then be adjusted to hit a desired alcohol level.
• Competition Preparation: Verify that a beer or wine's ABV falls within the range specified by BJCP or other style guidelines.
• Calorie Tracking: Estimate the calorie content of a 12-ounce serving for health-conscious brewers or those managing dietary intake.
• Education: Fermentation converts sugar into alcohol and carbon dioxide; the step-by-step formula view shows the mathematical relationship between gravity readings and ABV.
• Quality Control: Identify stuck fermentations early by comparing the expected FG to the actual reading. Low attenuation values may indicate yeast health issues or fermentation temperature problems.