🍺 Original Gravity to ABV Calculator
Enter your original gravity (OG) and final gravity (FG) readings to calculate the alcohol by volume (ABV) of your homebrew.
The two numbers this page returns
It uses the common ABV approximation — the gravity drop times 131.25 — and the standard apparent attenuation figure alongside it:
ABV % = (OG - FG) × 131.25
apparent attenuation %= (OG - FG) / (OG - 1) × 100The defaults, 1.050 down to 1.010, give 0.040 × 131.25 = 5.25% ABV and 0.040 / 0.050 = 80.0% attenuation. A barley wine from 1.100 to 1.020 gives 10.50% and the same 80.0%, because attenuation measures the fraction of the original sugar consumed, not the strength.
131.25 is an approximation, not physics. It fits ordinary-strength beer to within about a tenth of a per cent, and reads progressively high past roughly 1.070 OG, where the alcohol already in solution changes how the remaining sugar affects density. Above 8% ABV treat the answer as a close estimate.
Typical readings
| OG | FG | ABV | Attenuation |
|---|---|---|---|
| 1.040 | 1.010 | 3.94% | 75.0% |
| 1.050 | 1.010 | 5.25% | 80.0% |
| 1.060 | 1.012 | 6.30% | 80.0% |
| 1.090 | 1.022 | 8.93% | 75.6% |
Most ale yeasts land at 70-80% apparent attenuation. Much under 60% points at a stuck fermentation, a mash held too warm, or an under-pitch; over 90% suggests a highly attenuative or wild strain. OG must be greater than FG or the page returns an error.
Frequently asked questions
What ABV is 1.050 down to 1.010?
5.25%. The gravity fell 40 points, and 0.040 × 131.25 is 5.25. Beers that finish at 1.010 from a 1.050 start are the standard pale ale shape.
Is the ×131.25 formula accurate?
It is an approximation. Under about 1.070 OG it is within roughly 0.1% of the more elaborate formulas; for strong beer and wine it overstates the result by a few tenths, so a 12% calculation might really be 11.5%.
What does apparent attenuation mean?
The share of original gravity points the yeast removed. It is called apparent because alcohol is lighter than water, so the hydrometer exaggerates the drop; real attenuation is about four fifths of the figure shown.