ABV Calculator.
Calculate alcohol by volume from original and final gravity. Shows both the simple formula (the everyday homebrew shortcut) and the alternate formula (more accurate above 6% ABV and in the wine and mead range), along with apparent attenuation. Accepts specific gravity, Brix, or Plato.
Inputs
Enter your hydrometer or refractometer readings.
How this is calculated.
Show the formulas, derivation, and citations
Simple formula — the homebrew default. Accurate to about 6% ABV; underestimates above that.
Alternate formula — derived from Balling's relationship between extract and alcohol. Preferred above 6% ABV, including most wine and mead.
Apparent attenuation — the percentage of original sugars consumed by the yeast.
Unit conversions — Brix → SG uses the Lincoln Equation; Plato → SG uses the standard division by 250.
Worked example.
OG 1.064 · FG 1.012
Simple: (1.064 − 1.012) × 131.25 = 6.83% ABV.
Alternate: (76.08 × 0.052 / 0.711) × (1.012 / 0.794) = 7.09% ABV.
Apparent attenuation: 0.052 / 0.064 × 100 = 81.2%.
At this gravity the two formulas agree to within 0.3%. The spread widens to roughly 1% at OG 1.090, which is the practical reason to switch above 6% ABV.
Common mistakes.
- Using a refractometer for final gravity without correction. Refractometer readings drift in the presence of alcohol. Use a hydrometer for FG, or correct the refractometer value first.
- Not temperature-correcting the hydrometer reading. Most hydrometers are calibrated at 20 °C / 68 °F. A reading taken at 30 °C reads about 0.0012 SG low — small, but enough to skew the ABV by 0.15%.
- Assuming the simple formula is universal. It is fine up to about 6% ABV. For barley wine, imperial stouts, mead, wine, and ice cider, switch to the alternate formula or you will under-report alcohol.
- Treating apparent attenuation above 100% as a real number. Real attenuation is always lower than apparent. AA % > 100 means a measurement error in OG or FG, or a sample contaminated with super-attenuating wild yeast.
Related calculators.
Frequently asked.
When should I use the alternate formula instead of the simple one?
Above roughly 6% ABV, the simple formula begins to underestimate. For wines, meads, imperial stouts, and other high-gravity ferments, the alternate formula accounts for the non-linear relationship between gravity drop and alcohol production at higher sugar concentrations.
What is apparent attenuation?
The percentage of original sugars the yeast has consumed, calculated from the apparent gravity drop. Typical homebrew yeasts attenuate 70–80%; wine yeasts 95–100%. Lower than expected attenuation often signals a stuck fermentation.
Can I use a refractometer reading after fermentation?
Not directly. Refractometer readings drift in the presence of alcohol and must be corrected before they are usable as a final gravity value. Use a hydrometer for FG, or apply a refractometer correction first.
Why do the two formulas give different answers?
The simple formula is a linear approximation that works well up to about 6% ABV. The alternate, derived from Balling's work, adjusts for the non-linear relationship at higher gravities. The difference is small at session-strength gravities but grows above 1.080 OG.