Calculator
ABV calculator
How strong is the beer I brewed?
Strength is worked out from how much sugar the yeast removed, not measured directly. You take a gravity reading before fermentation and another after it, and the difference tells you how much sugar became alcohol. There is no household instrument that measures alcohol itself.
That indirect route is why two formulas exist. The simple one is a straight multiplication that is accurate to about 7% ABV and drifts high above it, and it is nonetheless the formula most calculators use without saying so. Both are offered here with their working shown, because a brewer who knows their answer rests on an empirical factor is better placed than one handed a number to three decimal places.
Result
- ABV5.5% ABV
- Simple formula5.4% ABV
- Alcohol by weight4.4%
- Apparent attenuation78.8%
Working
ABV = (76.08 × (OG − FG) ÷ (1.775 − OG)) × (FG ÷ 0.794)
| Step | Expression | Value |
|---|---|---|
| Gravity drop | OG − FG | 0.0410 |
| Simple estimate | (OG − FG) × 131.25 | 5.38% |
| Numerator | 76.08 × (OG − FG) | 3.1193 |
| Denominator | 1.775 − OG | 0.7230 |
| Correction factor | FG ÷ 0.794 | 1.2733 |
What it means
The two formulas agree closely at session strengths and diverge as gravity rises. Where they differ, the second figure is the more reliable one.
Worked example
The example above starts from these values. It is rendered on the server, so the formula, assumptions and limitations are all present whether or not you change anything.
- Result5.5% ABV
- Simple formula5.4% ABV
- Alcohol by weight4.4%
- Apparent attenuation78.8%
Inputs
| Original gravity | 1.052 |
|---|---|
| Final gravity | 1.011 |
How it is calculated
ABV = (76.08 × (OG − FG) ÷ (1.775 − OG)) × (FG ÷ 0.794)
What each term means
| OG | Original gravity — the density of the wort before fermentation |
|---|---|
| FG | Final gravity — the density of the beer after fermentation |
| 0.794 | Specific gravity of ethanol relative to water |
Step by step
| Step | Expression | Value |
|---|---|---|
| Gravity drop | OG − FG | 0.0410 |
| Simple estimate | (OG − FG) × 131.25 | 5.38% |
| Numerator | 76.08 × (OG − FG) | 3.1193 |
| Denominator | 1.775 − OG | 0.7230 |
| Correction factor | FG ÷ 0.794 | 1.2733 |
What this assumes
- Both gravity readings were taken at, or corrected to, the hydrometer’s calibration temperature.
- Fermentation is complete, so final gravity is stable.
Where it stops being reliable
- Both formulas are empirical approximations, not exact chemistry. The only way to know a beer’s ABV precisely is laboratory analysis.
- The simple formula, (OG − FG) × 131.25, drifts increasingly low above roughly 7% ABV. Most online calculators use it without saying so.
- Neither formula accounts for unfermentable sugars added after fermentation, such as lactose or priming sugar.
- A refractometer reading taken after fermentation must be corrected before use here — alcohol distorts refractive index. See the refractometer correction calculator.
What the number means
The two formulas agree closely at session strengths and diverge as gravity rises. Where they differ, the second figure is the more reliable one.
Empirical approximation. A curve fitted to measured data. It has real error bars, and it is frequently quoted as though it were exact.
Sources: Standard brewing practice; see the BeerHQ sources registry for the underlying texts.