Which ABV formula do you use?

We provide both the standard homebrewing formula ABV = (OG − FG) × 131.25 and an advanced formula more accurate at higher gravities: ABV = (76.08 × (OG − FG) / (1.775 − OG)) × (FG / 0.794).

Can I enter values in °Plato or Brix?

Yes. You can switch between SG and °Plato. For refractometers, enter pre- and post-fermentation Brix with a Wort Correction Factor to correct the final gravity.

Do you correct for hydrometer temperature?

Optionally yes. Provide the reading temperature and your hydrometer's calibration temperature to apply correction before computing ABV.

ABV (Alcohol By Volume) — rigorous calculation and guidance

This calculator implements both the widely used homebrewing equation and a more accurate high‑gravity formula. It also provides optional hydrometer temperature and refractometer (Brix) corrections, and reports alcohol by weight (ABW) and apparent attenuation. Each step and formula is documented for transparency and repeatability.

Formulas used

1) Standard homebrewing ABV (good for typical strength beers):

$$ \mathrm{ABV_{std}(\%)} = (\mathrm{OG} - \mathrm{FG}) \times 131.25 $$

Derivation uses stoichiometry of fermentation and ethanol density $(\rho_{EtOH} \approx 0.789\,\mathrm{g/mL})$. See discussion in industry references.

2) Advanced ABV (recommended for higher gravities):

$$ \mathrm{ABV_{adv}(\%)} = \left(\frac{76.08\,(\mathrm{OG}-\mathrm{FG})}{1.775-\mathrm{OG}}\right)\times \left(\frac{\mathrm{FG}}{0.794}\right) $$

This empirical relationship improves accuracy for high‑gravity fermentations by accounting for changing density across the range.

3) Alcohol by weight (ABW) from ABV:

$$ \mathrm{ABW(\%)} \approx \frac{\mathrm{ABV}}{0.789 + 0.211\,\mathrm{ABV}} $$

Uses the density of ethanol; suitable for brewing-strength ranges.

4) Apparent attenuation (from SG):

$$ \mathrm{AA(\%)} = \frac{\mathrm{OG}-\mathrm{FG}}{\mathrm{OG}-1} \times 100 $$

Shows the apparent percentage of fermentable extract consumed (uncorrected for alcohol).

5) SG ⇄ °Plato (cubic fit used in brewing practice):

$$ \begin{aligned} \mathrm{SG}(P) &= 1 + \frac{P}{258.6 - (P/258.2)\times 227.1} \\ P(\mathrm{SG}) &= -616.868 + 1111.14\,\mathrm{SG} - 630.272\,\mathrm{SG}^2 + 135.997\,\mathrm{SG}^3 \end{aligned} $$

Glossary

OG (Original Gravity): density of wort before fermentation (SG or °P).
FG (Final Gravity): density after fermentation (SG or °P). May be corrected for temperature or refractometer bias.
ABV: alcohol fraction by volume at 20 °C.
ABW: alcohol fraction by weight; useful for some regulatory contexts.
Apparent Attenuation: percentage drop in extract based on SG, not accounting for alcohol’s lower density.
WCF: Wort Correction Factor to correct refractometer readings in wort vs. sucrose.

Worked example

Suppose $\mathrm{OG}=1.060$ and $\mathrm{FG}=1.012$ (both at 20 °C):

Standard ABV: $\; (1.060-1.012)\times 131.25 = 6.30\%$.

Advanced ABV: $\; \left(\tfrac{76.08\times 0.048}{1.775-1.060}\right)\times \left(\tfrac{1.012}{0.794}\right) \approx 6.35\%$.

ABW: $\; \tfrac{6.35}{0.789+0.211\times 6.35} \approx 5.0\%$; Apparent Attenuation: $\; \tfrac{0.048}{0.060}\times 100 = 80\%$.

Authoritative sources

Alternate “advanced” ABV formula as used in industry calculators. BrewersFriend ABV Calculator.
Discussion of 131.25 factor via stoichiometry and ethanol density. Grainfather Help — Calculation: ABV.
SG ↔ °Plato relationships used in brewing practice. BrewersFriend — Plato ⇄ SG.
Definition of ABV and ethanol density. Wikipedia — Alcohol by volume.
ASBC (American Society of Brewing Chemists) reference methods and tools library for alcohol and extract analysis. ASBC Beer Methods & ASBC Tools.

FAQ

Should I use the standard or advanced ABV?

For most ales and lagers up to ~7% ABV, the standard equation is fine. Above that, or for very high OG, prefer the advanced formula.

How accurate are refractometer corrections?

They are estimates that depend on your WCF and measurement technique. If possible, confirm final gravity using a temperature‑corrected hydrometer.