Case 1
- Original gravity (OG)
- 1.05
- Final gravity (FG)
- 1.01
5.25%
Open with these valuesABV Calculator
5.25%
Result: 5.25 %The alcohol in a fermented drink is read off how far the specific gravity fell while the yeast worked: subtract the final reading from the original one and multiply by 131.25. A beer from 1.050 down to 1.010 lands at 5.25 % ABV. The factor is a homebrewing convention and holds to roughly 8 %.
The numbers at a glance
Held fixed: Original gravity (OG) 1.050.
| Final gravity (FG) | Result (%) |
|---|---|
| 0.940 | 14.44 |
| 0.960 | 11.81 |
| 0.980 | 9.19 |
| 1.000 | 6.56 |
| 1.010Your value | 5.25 |
| 1.020 | 3.94 |
| 1.040 | 1.31 |
Worked examples
Case 2
- Original gravity (OG)
- 1.06
- Final gravity (FG)
- 1.012
6.30%
Open with these valuesCase 3
- Original gravity (OG)
- 1.08
- Final gravity (FG)
- 1.02
7.88%
Open with these valuesHow it's calculated
ABV % = (OG − FG) × 131.25
- StepTake a hydrometer reading before pitching the yeast — the original gravity.
- StepTake a second reading once fermentation has stopped — the final gravity.
- ResultSubtract the second from the first and multiply the drop by 131.25.
What this number means
One formula among several
This calculator uses (OG − FG) × 131.25. Other empirical forms take about 131 for beer and 136 for wine, and one published table lets the factor drift from 133 to 137 as the drop grows.
The linear factor gives out around 8 %
Above roughly 8 % ABV it overstates the result, and brewers switch to fuller equations. It is a homebrewing convention, not a measured constant.
Both readings at the same temperature
Temperature shifts the gravity. Take both readings at the hydrometer's calibration temperature — one before pitching the yeast, one after fermentation has stopped.
A negative result is not a bug
The density has to fall during fermentation, so a final gravity above the original one comes back below zero. That means something went wrong or was misread, and the calculator does not hide it.
Commonly misread
Every ABV calculator should return the same number.
The 131.25 factor is one convention among several, with roughly 131 for beer and 136 for wine also in use. The same two readings can come out differently.
I can work out my 13 % wine with this.
The simple gravity formula is not built for that range. Above roughly 8 % the linear factor overstates the result.
I took the first reading once fermentation was already going.
The original gravity is the reading taken before the yeast is pitched. Once fermentation has started, part of the drop is already gone.
Reference table
| OG, FG | Typical brew | ABV |
|---|---|---|
| 1.040, 1.008 | Light lager | 4.20 |
| 1.050, 1.010 | Standard ale | 5.25 |
| 1.060, 1.012 | Strong ale | 6.30 |
| 1.080, 1.020 | Imperial stout | 7.88 |
| 1.050, 1.050 | Nothing fermented | 0.00 |
Questions
How do I calculate ABV from gravity readings?
Subtract the final gravity from the original gravity and multiply the drop by 131.25. A beer that started at 1.050 and finished at 1.010 gives (1.050 − 1.010) × 131.25 = 5.25 % ABV.
What are original gravity and final gravity?
Original gravity is the reading taken before fermentation, when the wort is still full of sugar. Final gravity is the reading taken after fermentation, once the yeast has turned that sugar into alcohol and carbon dioxide. The gap between the two is what the formula turns into a percentage.
Why does the gravity drop during fermentation?
Sugar is denser than water, so unfermented wort floats a hydrometer higher than plain water does. As the yeast eats the sugar and makes lighter alcohol, the liquid gets less dense and the reading falls. A final gravity above the original one means something went wrong, and the result then comes back negative.
What is a typical ABV for beer?
Most everyday beers land between 4 % and 6 %. Light lagers sit near 4 %, ales and pilsners around 5 %, and strong IPAs climb past 7 %. Wine is usually 11 to 14 %, which the simple gravity formula is not built for.
How accurate is the 131.25 factor?
It is a standard approximation, reliable for typical beers up to roughly 8 % ABV. Above that the linear factor overstates the result and brewers switch to fuller equations. Take both readings at the hydrometer's calibration temperature, because temperature shifts the gravity.
Sources and last check
Information, not professional advice.