How to use the ABV calculator
- Take an original gravity (OG) reading with a hydrometer before adding yeast.
- When fermentation has finished (the same reading on two or three days in a row), take the final gravity (FG).
- Enter both readings as specific gravity (e.g. 1.050) or in °Plato/Brix.
- Read the ABV, the alternate ABV for strong drinks, and the apparent attenuation.
ABV formulas
Standard: ABV % = (OG − FG) × 131.25 Alternate: ABV % = 76.08 × (OG − FG) ÷ (1.775 − OG) × (FG ÷ 0.794) ABW % = ABV × 0.79336 ÷ FG Attenuation = (OG − FG) ÷ (OG − 1) × 100
Worked example
A pale ale with OG 1.050 and FG 1.010:
- ABV = (1.050 − 1.010) × 131.25 = 5.25%
- Alternate formula = 5.34%
- Attenuation = 0.040 ÷ 0.050 = 80%
Typical gravities and strengths
| Drink | Typical OG | Typical FG | ABV |
|---|---|---|---|
| Light lager | 1.040 | 1.008 | 4.2% |
| Pale ale / IPA | 1.050–1.065 | 1.010–1.014 | 5.3–6.7% |
| Stout | 1.045–1.075 | 1.010–1.018 | 4.6–7.5% |
| Barleywine | 1.090–1.110 | 1.020–1.030 | 9.2–10.5% |
| Cider | 1.045–1.055 | 0.998–1.004 | 5.4–7.5% |
| Dry wine | 1.085–1.095 | 0.990–0.996 | 11.7–13.8% |
ABV values use the standard formula and are rounded; the alternate formula gives slightly higher numbers for strong drinks.
Why the gravity drops
Specific gravity compares the density of your liquid with water (1.000). Sugar dissolved in wort or juice makes it denser, so the original gravity is above 1.000. As yeast ferments, it turns sugar into alcohol and carbon dioxide. The sugar disappears and alcohol, which is lighter than water (about 0.79 g/mL), takes its place, so the gravity falls. Dry wines and ciders can finish below 1.000 for exactly that reason. The bigger the drop from OG to FG, the more sugar became alcohol.
Kombucha, mead and fruit wines
The same calculator works for any fermented drink. Mead and fruit wines often start between 1.080 and 1.120, so use the alternate ABV figure. Kombucha usually has very little alcohol (often below 1–2%), and second-fermentation sugar or fruit can raise it. If you add sugar partway through fermentation, add the gravity points that sugar contributes to your original gravity, or your ABV will read too low.
Tips for accurate readings
- Spin the hydrometer to shake off bubbles, and read at the bottom of the curve (meniscus) at eye level.
- Degas fizzy samples such as cider or kombucha by stirring, or bubbles will lift the hydrometer.
- Correct for temperature — a sample 10 °C warmer than calibration reads about 0.002 low.
- Priming sugar for bottle conditioning adds about 0.2–0.3% ABV.
- Write readings down with the date and temperature in a brew log, so you can repeat good batches and spot stuck fermentations early.
- Check your local laws on home brewing and home distillation, which vary widely between countries.