ABV Calculator
Estimate beer alcohol by volume from original and final specific gravity readings.
Last updated · View algorithm, constants and default inputs (JSON)
About this calculator
The common homebrewing estimate multiplies the specific-gravity drop by 131.25. It is approximate, especially for stronger beers. The drink count uses a U.S. 14 g standard-drink definition and a fixed 330 mL serving.
Worked example
calculated with the default values below
Original gravity 1.05 SG · Final gravity 1.01 SG Alcohol by volume 5.25 % · Alcohol by weight 4.17 % · Apparent attenuation 80.0 % · U.S. standard drinks per 330 mL (14 g each) 0.98 drinks
General background references
Disclaimer
These calculators give general cooking guidance. Ingredient density, oven calibration, altitude and equipment all vary, and safe minimum internal temperatures always take precedence over timings. Follow the food-safety advice issued by your national authority.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
ABV = (OG − FG) × 131.25
- ABV
- alcohol by volume (%)
- OG
- original gravity
- FG
- final gravity
Specific gravity readings are dimensionless (for example, 1.050 and 1.010). ABV is a homebrewing approximation; ABW uses a fixed conversion approximation. The displayed drink count assumes a 330 mL serving and the U.S. 14 g definition.
Frequently asked questions
Why does the 131.25 multiplier estimate alcohol from gravity drop?
Fermentation converts sugar to ethanol and carbon dioxide, and the gravity drop tracks sugar consumed. Multiplying (OG − FG) by 131.25 is the standard approximation tying that drop to alcohol by volume for wort near typical strength. It drifts above about 10% ABV, where the real relationship is non-linear; for high-gravity beers use a refractometer correction or lab test instead.