ABV Calculator
Alcohol by volume (ABV) is the percentage of a beer's volume that is ethanol, calculated from the drop in specific gravity during fermentation. The standard estimate is ABV = (OG − FG) × 131.25, accurate below about 1.070. For stronger worts, ABV = 76.08 × (OG − FG) / (1.775 − OG) × (FG / 0.794) corrects for the density shift ethanol introduces.
Enter the original gravity you measured before pitching and the final gravity after fermentation. Everything else follows from those two numbers.
How ABV is calculated
Fermentation turns sugar into alcohol and CO2. Sugar is denser than water and alcohol is lighter, so the gravity of the wort falls as it ferments. The size of that fall is what tells you how much alcohol is there.
The quick formula everyone learns first is:
ABV = (OG − FG) × 131.25
It is close enough for ordinary strength beer and wrong by a noticeable margin above about 1.070. This calculator uses the more accurate form, which is what Brewgravity uses inside the app too:
ABV = 76.08 × (OG − FG) / (1.775 − OG) × (FG / 0.794)
For a 1.055 to 1.012 beer the two agree to within about a tenth of a percent. For a 1.100 barleywine the simple formula overstates the result.
Worked examples
Typical gravity pairs, with the numbers this calculator produces:
| OG | FG | ABV | Attenuation | Cal / 12 oz |
|---|---|---|---|---|
| 1.040 | 1.008 | 4.2% | 80% | 139 |
| 1.048 | 1.010 | 5.1% | 79% | 165 |
| 1.055 | 1.012 | 5.8% | 78% | 188 |
| 1.062 | 1.014 | 6.5% | 77% | 210 |
| 1.070 | 1.016 | 7.5% | 77% | 236 |
| 1.090 | 1.020 | 10.0% | 78% | 298 |
ABV, ABW and attenuation
ABV is alcohol as a proportion of the volume of beer, and it is what goes on a label. ABW is alcohol by weight, always the smaller number because ethanol is less dense than water — roughly ABV × 0.79.
Apparent attenuation is the proportion of the original gravity points the yeast removed: (OG − FG) / (OG − 1). It is “apparent” because the hydrometer is reading a mixture of water, alcohol and residual sugar, and the alcohol drags the reading below what the sugar alone would give. Most ale yeasts land between 70% and 80%.
Getting an accurate reading
- Hydrometers are calibrated at a specific temperature, usually 20 °C or 60 °F. A warm sample reads low.
- A refractometer cannot be read directly once fermentation has started — alcohol changes how the sample refracts light. Use the refractometer correction calculator instead.
- Take the OG after the wort is fully mixed and cooled. A sample from the top of an unmixed fermenter can be several points out.
ABV Calculator — questions
What is a normal final gravity?
For most ales, 1.008 to 1.016. It depends on the yeast's attenuation and how fermentable the wort is — a mash at 62 °C produces a much more fermentable wort than one at 70 °C, so the same recipe can finish several points apart.
Why is my ABV lower than expected?
Usually the fermentation stalled or the mash was less fermentable than planned. Check the final gravity against the yeast's stated attenuation: if the yeast claims 75% and you got 65%, the beer has stopped early rather than the calculation being wrong.
Which ABV formula is correct?
Both are approximations of the same thing. The simple (OG − FG) × 131.25 form is fine below about 1.070; above that the alternative formula used here tracks reality more closely.
ABV that updates as you build the recipe
Brewgravity predicts ABV live from your grain bill and yeast choice — no retyping OG and FG into a separate page. The free plan has no recipe limit.
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