ABV Calculator

How to Calculate ABV from Gravity Readings

This ABV calculator uses your original gravity (OG) and final gravity (FG) readings to compute alcohol by volume — the same method homebrewers and professional brewers use to verify fermentation results. The difference between OG and FG tells you how much sugar was consumed by yeast and converted to alcohol and CO₂.

The simplest formula is: ABV% = (OG − FG) × 131.25. This works well for beers with ABV under 8%. For higher-gravity beers, the alternate formula provides better accuracy because it accounts for the changing density as alcohol is produced.

Which ABV Formula Is Most Accurate?

Three formulas are commonly used in brewing:

• Basic: (OG − FG) × 131.25 — easiest, accurate for session beers
• Alternate: (76.08 × (OG − FG)) / (1.775 − OG) × (FG / 0.794) — best for high-gravity beers
• Simple: (OG − FG) / 0.00753 — quick approximation used by some homebrewers

All three produce nearly identical results for standard-strength beers. The alternate formula is most accurate above 8% ABV because it accounts for the non-linear relationship between density and alcohol content.

Standard Drinks and Alcohol Content

The NIAAA defines one US standard drink as 14 grams of pure alcohol. Many craft beers, double IPAs, and cocktails exceed one standard drink per serving. Knowing the ABV and serving size lets you calculate exactly how many standard drinks you are consuming.

Formula: Standard drinks = (Volume in mL × ABV% × 0.789) ÷ 14. The 0.789 factor is the density of ethanol in g/mL. For example, 16 oz (473 mL) of a 7% IPA: 473 × 0.07 × 0.789 ÷ 14 ≈ 1.87 standard drinks.

Calories from Alcohol

Ethanol contains 7 kcal per gram — nearly twice the calorie density of carbohydrates or protein. In a 12 oz beer at 5% ABV, alcohol alone contributes about 98 calories. The remaining calories come from residual malt sugars and other carbohydrates. For reference, a 5 oz glass of 12% wine has about 14g of alcohol for roughly 98 alcohol-derived calories, plus carbohydrate calories from residual sugars.

ABV Labeling Requirements

In the United States, the TTB (Alcohol and Tobacco Tax and Trade Bureau) requires ABV labeling on all alcoholic beverages. Beer is allowed a ±0.3% tolerance for ABV claims on labels. Wine and spirits have stricter labeling standards. Our sobriety calculator can help track time since last drink, and the EtG calculator estimates alcohol detection windows for drug testing purposes.

ABV and Blood Alcohol Content — What the Numbers Mean

ABV tells you how much alcohol is in a drink; Blood Alcohol Content (BAC) tells you how much alcohol is in your bloodstream after you drink it. The two are related but different. The US legal driving limit is 0.08% BAC, and even lower BAC levels (0.02–0.05%) impair reaction time and judgment.

The body processes approximately one standard drink per hour regardless of body size, hydration, or caffeine intake. Knowing a drink's ABV and serving size allows you to count standard drinks accurately — critical for responsible consumption. A craft IPA at 8% ABV in a 16 oz pour contains 2.4 standard drinks, not one.

Fermentation Attenuation and Residual Sweetness

Apparent attenuation is the percentage of fermentable sugars the yeast consumed during fermentation: Attenuation% = (OG − FG) / (OG − 1.000) × 100. A highly attenuated beer (80%+) is drier and crisper; a low-attenuation beer (60–70%) retains more residual sweetness. Most ale yeasts attenuate 72–82%; lager yeasts tend toward 78–85%; Belgian and saison yeasts can exceed 85% attenuation.

Understanding attenuation helps homebrewers troubleshoot stuck fermentations, dial in dryness, and predict the final flavor profile of their beer. If your FG is higher than expected, fermentation may not be complete — check the gravity on consecutive days before concluding.