Alcohol By Volume (ABV) Calculator
Work out the alcohol by volume of your beer, wine, cider or mead from a pair of specific-gravity readings — using both the popular simple formula and the more accurate advanced (Hall) formula used for high-gravity brews.
Alcohol by volume (advanced)
5.79%
- ABV (simple formula)
- 5.64%
- Alcohol by weight (ABW)
- 4.58%
- Apparent attenuation
- 78.18%
ABV is derived from the drop in specific gravity during fermentation. The simple formula, ABV% ≈ (OG − FG) × 131.25, is fast and accurate to about 6%. The advanced (Hall) formula corrects for non-linearity at high gravity and is preferred for IPAs, barleywines and meads. Alcohol by weight is roughly ABV × 0.79; apparent attenuation is the fraction of sugar the yeast appears to have consumed.
How to use this calculator
Take a hydrometer or refractometer reading of the wort or must before pitching yeast — this is your original gravity (OG), a value like 1.055. After fermentation has finished and the gravity has stabilised for at least two days, take another reading — this is your final gravity (FG), usually between 0.995 and 1.020. Type both numbers into the calculator. You will get ABV calculated two ways — the simple Daniels-style formula and the advanced Hall formula — plus alcohol by weight and apparent attenuation. Use the advanced ABV for any brew likely to exceed 6%; the simple formula systematically under-estimates strong beers, wines and meads.
How the calculation works
During fermentation, yeast consume sugar (which makes the liquid denser than water) and produce ethanol and CO₂ (ethanol is less dense than water). The bigger the gap between OG and FG, the more sugar was converted and the more alcohol produced. The simple formula, ABV% = (OG − FG) × 131.25, is a linear approximation derived from typical beer-strength brews and is widely taught because it can be done in your head. The advanced (Hall) formula, ABV% = (76.08 × (OG − FG) / (1.775 − OG)) × (FG / 0.794), corrects for the non-linear relationship between extract consumption and alcohol production at high gravity. Apparent attenuation is the percentage of fermentable extract the yeast consumed: (OG − FG) / (OG − 1).
Worked example
A standard pale ale ferments from OG 1.055 to FG 1.012. The simple formula gives (1.055 − 1.012) × 131.25 = 0.043 × 131.25 = 5.64% ABV. The advanced formula gives (76.08 × 0.043 / 0.720) × (1.012 / 0.794) = 4.544 × 1.275 = 5.79% ABV — close at this strength. A barleywine going OG 1.100 → FG 1.020 shows the divergence: simple gives 10.50%, advanced gives 11.58% — a meaningful difference once you cross 8%. Alcohol by weight is roughly 79% of ABV: 5.79% ABV ≈ 4.57% ABW. Apparent attenuation for the pale ale is 0.043 / 0.055 = 78%, healthy for a clean ale yeast.
Frequently asked questions
What is the formula for ABV from gravity?
The simple formula is ABV% = (original gravity − final gravity) × 131.25. So a beer that goes from 1.050 to 1.010 has an ABV of (1.050 − 1.010) × 131.25 = 5.25%. This is accurate to about 6% ABV. For stronger brews, use the advanced (Hall) formula: ABV% = (76.08 × (OG − FG) / (1.775 − OG)) × (FG / 0.794), which compensates for the non-linearity at high gravity.
Which ABV formula should I use — simple or advanced?
Use the simple formula for everyday session beers, ciders and light wines under 6% ABV — it is accurate enough and trivial to do in your head. Use the advanced (Hall) formula for IPAs, barleywines, high-ABV ciders, fruit wines and meads, where the simple formula will under-estimate the true alcohol content by 0.5–1% ABV. Commercial breweries are required to report directly measured ethanol; homebrewers use these formulas because direct ethanol measurement requires distillation or specialist instruments.
What is the difference between ABV and ABW?
ABV (alcohol by volume) is the percentage of the liquid that is ethanol by volume. ABW (alcohol by weight) is the percentage by mass. Because ethanol is less dense than water (0.789 g/mL at 20°C), ABW is always smaller than ABV — roughly ABW = ABV × 0.79. So a 5% ABV beer is about 4% ABW. The US once labelled beer in ABW (which made everything look weaker), but switched to ABV in the 1990s to align with the rest of the world.
What is apparent attenuation?
Apparent attenuation is the percentage of starting extract the yeast appears to have consumed, calculated as (OG − FG) / (OG − 1). For a beer fermenting from 1.050 to 1.010, that is 40/50 = 80% apparent attenuation. Most ale yeasts achieve 70–80% apparent attenuation; lager and saison yeasts can hit 85–90%. It is called "apparent" because residual ethanol — which is less dense than water — pulls the FG reading lower than the true sugar content suggests. Real attenuation, which corrects for this, is roughly 0.81 × apparent attenuation.
Why does my calculated ABV differ from the label?
Commercial breweries measure ABV directly by distillation or near-infrared spectroscopy, not by gravity drop. The gravity-based formulas assume normal sugar fermentation; if the brewer added a non-fermentable sugar, force-carbonated with sucrose, back-sweetened, or used a non-Saccharomyces yeast, the calculation will be off. Hydrometer accuracy (calibration temperature, foam, sample temperature) also adds 0.1–0.3% ABV of noise. For homebrew use, expect the calculator to land within 0.3% of the actual ABV when both readings are taken correctly.
Do I need to correct gravity for temperature?
Yes, for hydrometer readings. Hydrometers are calibrated for a single temperature — usually 20°C (68°F) or 15.5°C (60°F). A reading taken at 30°C will be lower than the true gravity by about 0.001–0.002 SG. Either cool the sample to the calibration temperature or apply a correction (most hydrometers ship with a correction chart). Refractometers also need correction, but they additionally need a separate correction for the presence of alcohol once fermentation has started — a known source of error for ABV calculated from refractometer FG readings.