How to use this calculator
- Measure the original gravity (OG) of the wort or must before pitching yeast.
- When fermentation is complete — the same reading on two or three consecutive days — measure the final gravity (FG).
- If either sample was not at your hydrometer's calibration temperature, correct it first.
- Enter both values as specific gravity, for example 1.050 and 1.010.
What the inputs mean
Specific gravity (SG) is the density of a liquid relative to water. Dissolved sugar raises it above 1.000; yeast converts that sugar into alcohol and carbon dioxide, and because alcohol is less dense than water the gravity falls. The drop from OG to FG is what the formulas use to estimate how much alcohol was produced.
Formulas
Standard formula, used by most homebrewing references:
ABV = (OG − FG) × 131.25Alternate formula, which accounts for the non-linear relationship at higher gravities:
ABV = 76.08 × (OG − FG) / (1.775 − OG) × (FG / 0.794)Apparent attenuation is the share of the original gravity points that fermentation removed:
Attenuation = (OG − FG) / (OG − 1) × 100Example
A pale ale with an OG of 1.050 finishes at 1.010. The standard formula gives (1.050 − 1.010) × 131.25 = 5.25 % ABV; the alternate formula gives 5.34 %. Apparent attenuation is 80 %.
Accuracy & limitations
- Both formulas are empirical approximations; treat the result as an estimate, and expect the two to diverge more as gravity increases.
- Sugar added after the OG reading (priming, fruit, step-feeding) is not counted. Add its gravity contribution to the OG.
- This is different from measuring a spirit with an alcoholmeter. For distilled spirits use the alcohol temperature correction calculator.
- Accepted ranges: OG 1.000–1.200, FG 0.980–1.200, and FG must be lower than OG.
FAQ
Which ABV formula should I use?
The standard formula, (OG − FG) × 131.25, is the one most homebrew software and recipes use and is fine for typical beers, ciders and wines. For high-gravity beers and meads the alternate formula gives a higher estimate and is often preferred. The gap between the two results is a useful reminder that both are approximations.
Do I need to correct gravity readings for temperature first?
Yes, if the sample was not at your hydrometer's calibration temperature. Correct both the original and final gravity with the hydrometer correction calculator, then enter the corrected values here.
Can I use refractometer readings?
Not directly. Once fermentation starts, alcohol distorts refractometer readings, so a final refractometer reading must be converted with a dedicated refractometer correction before it can be used as a final gravity.
Is this ABV accurate enough for labelling?
No. Gravity-based ABV is an estimate based on sugar consumed. For labelling or tax purposes, strength has to be measured with an approved method such as distillation followed by a density measurement.