This ABV calculator estimates the alcohol by volume of your beer, wine, cider or mead from hydrometer readings — original gravity before fermentation and final gravity after — with apparent attenuation and a calorie estimate alongside.
Both ABV formulas are shown because they diverge on strong drinks: the standard linear formula serves most beers; the alternate (used by many pro brewers) prices in the changing density relationships at high gravity. Hydrometers read in water-calibrated degrees — temperature-correct your readings (most are calibrated at 60 °F / 20 °C).
ABV = (OG − FG) × 131.25
Fermentation converts sugar (which raises gravity) into alcohol (which lowers it), so the gravity drop meters the alcohol made. The 131.25 constant bundles yeast’s conversion efficiency and ethanol’s density. The alternate formula — ABV = [76.08 × (OG − FG) ÷ (1.775 − OG)] × (FG ÷ 0.794) — corrects the drift at high gravities where the linear version under-reads. Part of our Food Calculators collection.
Worked Example (Verified)
- OG 1.050 → FG 1.010 (defaults): standard ABV = 0.040 × 131.25 = 5.25% — the archetypal pale ale; alternate formula reads 5.34% (they agree within a tenth at session strengths, as they should)
- Apparent attenuation: 0.040 ÷ 0.050 = 80% — a healthy, fairly dry finish for an ale yeast (65–70% reads sweet/full, 85%+ bone-dry)
- A barleywine at OG 1.100 → FG 1.020: standard says 10.50%, alternate ≈ 11.6% — the divergence is why both are printed once you leave lager gravity
- Wine math is the same river: grape must at 1.095 fermenting to 0.994 → ≈ 13.3% — though winemakers often quote from Brix (≈ × 0.55–0.59 potential-alcohol rule)
Reading Gravity Like a Brewer
- “Apparent” attenuation overstates sugar consumption because alcohol is less dense than water — real attenuation is ~0.82× the apparent figure; yeast datasheets speak apparent, so the dialect matches here.
- A stuck fermentation shows as FG plateauing high; the ABV of an unfinished beer is a progress report, not a result.
- Refractometers lie after fermentation starts (alcohol bends light differently) — their readings need correction formulas; hydrometer numbers feed this calculator directly.
- Priming sugar and bottle conditioning add ~0.2–0.5% ABV that the pre-bottling FG didn’t know about.
Related Tools
- BAC Calculator — where the finished product meets physiology
- Caffeine Calculator — the other great beverage molecule
- Food Calculators — the full collection
Frequently Asked Questions
How do you calculate ABV from gravity?
ABV ≈ (OG − FG) × 131.25. A beer dropping from 1.050 to 1.010 yields 5.25%. For high-gravity brews the alternate formula (shown alongside) corrects the linear approximation — they diverge by a full point or more at barleywine strength.
What is apparent attenuation?
The percentage of the gravity drop relative to the total extract: (OG − FG) ÷ (OG − 1) × 100. Typical ale yeasts attenuate 65–80% apparently; the number characterizes both the yeast strain and the wort’s fermentability (mash temperature shows up here).
ABV vs ABW — what’s the difference?
Alcohol by volume vs by weight. ABW = ABV × 0.789 ÷ FG (ethanol is lighter than beer, so ABW always reads lower — 5.25% ABV ≈ 4.1% ABW). US labels historically used ABW in some states, which is why older “3.2 beer” meant 3.2% ABW ≈ 4.0% ABV.
Can I calculate ABV without the original gravity?
Not from FG alone — the drop is the measurement. If you missed the OG, recipe software can estimate it from your grain bill and efficiency; finished-beer analysis (distillation or ebulliometer) is the lab route. Going forward: the hydrometer reading before pitching is the cheapest data in brewing.
How accurate is the 131.25 formula?
Within ~±0.2% ABV for typical beers — plenty for homebrew and recipe work. Commercial labeling tolerances are wider than the formula’s error. The inputs dominate accuracy: a 0.002 hydrometer misread swings the answer 0.26 points.
Is this ABV calculator free?
Yes — free, instant, no sign-up.