ABV Calculator (Alcohol by Volume)

Determining alcohol by volume relies on measuring the change in density of your liquid as yeast consumes sugars and produces ethanol and carbon dioxide. The calculation begins by estimating alcohol by weight (ABW) using the original extract (OE) and apparent extract (AE) values via the formula: ABW = (0.372 + 0.00357 × OE) × (OE - AE). Once ABW is established, the calculator applies a density correction factor relative to ethanol's specific gravity (approximately 0.7907 g/cm³) to derive the final ABV. Additionally, US proof is calculated simply by multiplying the ABV by 2, while total alcohol content is determined by multiplying the volume of the batch by the percentage of ABV.

Imagine you are brewing an all-grain American pale ale. Your initial hydrometer reading yields an original extract of 12.5 degrees Plato, and your final reading after fermentation gives an apparent extract of 3.0 degrees Plato. First, compute the alcohol by weight: ABW = (0.372 + (0.00357 × 12.5)) × (12.5 - 3.0), which results in an ABW of approximately 3.96%. Next, plug this figure into the ABV equation incorporating the apparent extract polynomial correction. The resulting alcohol by volume (ABV) is approximately 5.0%. To find the US proof, multiply 5.0 by 2, yielding 10-proof. Finally, if your total batch volume is 19 liters (5 gallons), the total pure alcohol content is 19 × (5.0 / 100) = 0.95 liters of pure ethanol.

Always calibrate your hydrometer or refractometer at the manufacturer's specified temperature (usually 60°F or 20°C) because temperature significantly alters liquid density and can distort your extract readings. When using a refractometer after fermentation has started, remember to apply a specialized correction formula, as alcohol refracts light differently than unfermented wort. Finally, ensure your sample is completely degassed before taking gravity readings, as trapped carbon dioxide bubbles can lift the hydrometer and lead to artificially high extract readings.