🍺 Beer ABV Calculator
Enter the original gravity (OG) before fermentation and the final gravity (FG) after fermentation to instantly get alcohol by volume (ABV), alcohol by weight (ABW), apparent and real attenuation, plus calories and carbohydrates per serving. Includes hydrometer temperature correction and beer style presets. All calculations run locally in your browser.
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❓ FAQ
What are OG and FG, and how do I measure them?
OG (Original Gravity) is the specific gravity of the wort before fermentation; FG (Final Gravity) is the gravity after fermentation is complete. Measure both with a hydrometer: take a wort sample before pitching yeast for OG, then sample again after fermentation finishes for FG. The difference represents the sugar consumed by yeast — the larger the drop, the higher the alcohol content. Remember to apply temperature correction (hydrometers are usually calibrated at 20°C).
How is ABV calculated? Why are there two formulas?
The most common simple formula is ABV = (OG − FG) × 131.25, which is accurate enough for most beers. The more precise cubic formula, ABV = (76.08 × (OG − FG) / (1.775 − OG)) × (FG / 0.794), corrects for the influence of alcohol on hydrometer readings and is more accurate for high-gravity (strong) beers. This calculator uses the cubic formula as the primary result and shows both in the formula box.
What is the difference between apparent and real attenuation?
Apparent attenuation uses hydrometer readings directly: (OG − FG) / (OG − 1). Alcohol skews hydrometer readings upward, so apparent attenuation overstates how much sugar yeast actually consumed. Real attenuation corrects for alcohol using the Balling formula (RE = 0.1808×OG°P + 0.8192×FG°P) and is approximately apparent attenuation × 0.82. Typical homebrew beers show 72%–85% apparent attenuation.
How are beer calories estimated?
Beer calories come mainly from alcohol (about 6.9 kcal per gram) and carbohydrates (about 4 kcal per gram). This tool first derives residual extract using the real-extract formula (RE = 0.1808×OG°P + 0.8192×FG°P), then combines ABW with the serving size to estimate alcohol and carb calories. Example: a beer with OG 1.050 / FG 1.010 has roughly 167 kcal per 12 oz, matching typical craft beer labels.