Alcohol by volume is not a mystery — it's straightforward arithmetic from two gravity
readings. Enter your original gravity and final gravity below and the calculator returns
ABV, apparent attenuation, and alcohol by weight. Every formula is shown in full, nothing
is hidden, and no figure is rounded away silently.
ABV from OG & FG·Apparent attenuation·Alcohol by weight (ABW)
Brew and drink responsibly
This calculator gives you informational arithmetic only — it is not a substitute for
laboratory ABV measurement. Homebrew gravity readings have real-world error margins
(see the FAQ). Always ferment and share homebrew in accordance with your local laws;
in the United States, homebrewing is federally legal for personal and household use
but commercial distribution without a license is not. This is not medical advice.
Please drink responsibly.
Enter your original gravity (before fermentation) and final gravity (after fermentation is complete). Results update as you type. Both values should be specific gravity hydrometer readings — for example, 1.050 and 1.010.
Gravity readings
Specific gravity of your wort before pitching yeast. Typical range: 1.030–1.090 for most homebrew styles. Measure after cooling the wort to near your hydrometer's calibration temperature.
Specific gravity once fermentation is stable — same reading two days in a row. Typically 1.005–1.020 for most beers. Must be lower than OG.
This batch is approximately ABV
Alcohol by Volume
Apparent Attenuation
Alcohol by Weight
The formulas, in full
Nothing here is a black box. These are the exact calculations the tool runs — the same
arithmetic you could do on paper or in a spreadsheet. The constant 131.25 is an empirical
factor relating the density difference between OG and FG to the ethanol content of the
finished beer; it is the standard used by the American Homebrewers Association.
How each number is derived
1 — Gravity points fermented (the foundation of all three outputs)
3 — Apparent attenuation (how much sugar the yeast consumed)
attenuation (%) = (OG − FG) ÷ (OG − 1) × 100
Example: 0.040 ÷ 0.050 × 100 = 80.00%
Note: (OG − 1) is the total fermentable potential in gravity points above water.
Attenuation of 75–85% is typical for most ale and lager yeast strains.
4 — Alcohol by Weight (ABW)
ABW (%) = ABV × ABW_RATIO where ABW_RATIO = 0.79336
Example: 5.25 × 0.79336 = 4.17%
The ratio 0.79336 is the standard ABV-to-ABW conversion factor, close to the specific gravity of ethanol (which is less dense than water,
so the same volume of alcohol weighs less, giving a lower percentage by weight).
OG, FG, and ABV reference for common beer styles
These are approximate typical ranges compiled from the BJCP Style Guidelines
and general homebrewing references. Your actual batch numbers will vary based on
grain bill, mash efficiency, yeast strain, and fermentation temperature. Use them
as a sanity check on your readings, not as targets to hit precisely.
Style
Typical OG
Typical FG
Approx. ABV
Attenuation note
American Light Lager
1.028–1.040
1.004–1.008
~3.2–4.2%
Very high attenuation (85–90%+); adjunct-heavy, highly fermentable wort.
~70–76%; English ale strains leave more body; fuller malt character.
American IPA
1.056–1.070
1.008–1.014
~5.5–7.5%
High attenuation (76–86%); dry hop forward, clean finish.
Stout (Dry Irish)
1.036–1.050
1.007–1.011
~4.0–5.0%
~76–82%; roasted barley contributes color and bitterness without fermentable sugar.
Belgian Tripel
1.075–1.085
1.008–1.014
~7.5–9.5%
~83–89%; Belgian strains and simple sugar additions drive very high attenuation.
German Hefeweizen
1.044–1.052
1.010–1.014
~4.9–5.6%
~73–78%; wheat malt adds protein haze and moderate unfermentables.
Imperial Stout
1.075–1.115
1.018–1.030
~8.0–12.0%
~72–80%; high residual gravity contributes body and sweetness to the finished beer.
All OG/FG/ABV figures are approximate and represent typical ranges; individual recipes,
mash temperatures, yeast strains, and fermentation conditions will produce results outside
these ranges. ABV calculated using (OG − FG) × 131.25. Attenuation figures are apparent
attenuation as defined by the formula above.
Why gravity readings are the right way to measure ABV
Density changes tell the story of fermentation. Water has a specific gravity of exactly
1.000. Wort is denser than water because of dissolved sugars; as yeast converts those
sugars to alcohol and CO₂, the liquid becomes less dense. The difference between your
starting and ending density is a direct measure of how much sugar was converted —
and therefore how much alcohol was produced.
OG sets the ceiling on ABV
Original gravity is a snapshot of how much fermentable sugar is in your wort before yeast does anything. A higher OG means more potential alcohol — but it does not guarantee it. Yeast health, pitch rate, fermentation temperature, and wort composition all affect whether you reach the potential ABV the OG implies. Think of OG as the maximum; FG tells you how close you got.
FG tells you whether fermentation finished
A stable FG — the same reading two days in a row — confirms fermentation is complete. An unexpectedly high FG (beer sweeter than the style suggests, lower ABV than calculated from OG and expected attenuation) usually means a stuck fermentation: yeast ran out of nutrients, got too cold, or the wort contained too many unfermentable dextrins from a high mash temperature. Raising the temperature by a few degrees and gently rousing the yeast are the first remedies to try.
Temperature correction matters more than most brewers think
Most hydrometers are calibrated at 60°F (15.6°C) or 68°F (20°C). Measuring warm wort — even at 80°F — introduces meaningful error. At 80°F, a reading that appears to be 1.050 on a 60°F-calibrated instrument is actually closer to 1.052. For typical homebrewing precision this is a small correction, but if you're hitting a gravity target for a competition batch it is worth accounting for. Cool your sample in an ice bath to near the calibration temperature before reading, or use a temperature correction table.
How to get accurate gravity readings
The formula is exact; the accuracy of the result depends on the accuracy of two numbers.
These steps address the most common sources of measurement error.
Cool your sample before measuring OG
After the boil, chill your wort to within a few degrees of your hydrometer's calibration temperature before taking the reading. A warm sample reads falsely low because the less dense hot wort floats the hydrometer higher — wait until your thermometer matches the calibration mark on the instrument.
Spin out CO₂ bubbles before reading FG
Actively fermenting or recently fermented beer contains dissolved CO₂ that clings to the hydrometer as tiny bubbles. These buoy the instrument up and make it read falsely high — giving you a FG that looks higher than it really is. Spin the hydrometer gently in your test tube to dislodge bubbles before reading. Taking the sample the day after fermentation visibly slows also helps.
Read the bottom of the meniscus at eye level
The surface of the liquid curves up where it meets the glass — the meniscus. Read the scale at the lowest point of that curve, with your eye at the level of the liquid surface. Reading from above or below the meniscus introduces consistent parallax error, typically 0.001–0.002 SG points, which shifts ABV by roughly 0.1–0.25%.
Confirm FG is stable over two consecutive days
Do not rely on a single FG reading. Measure on day one; if the reading is the same on day two, fermentation is done. A drop of even 0.002 SG between days means yeast is still working and your ABV will be higher than the current reading predicts. Packaging prematurely risks over-carbonation or bottle bombs.
Use a hydrometer for FG, not a refractometer
Refractometers are calibrated for pure sugar solutions. In finished beer, alcohol changes how light bends through the sample, making the refractometer read a falsely high FG. Reserve refractometers for quick OG checks during or just after the boil; always use a hydrometer for final gravity on fermented beer unless you apply a validated correction formula.
Where to buy
Got your numbers? Here's where to pick up what you need:
The units and terms that appear on a hydrometer, a recipe, or a style guideline —
in plain English.
Original Gravity (OG)
The specific gravity of your wort measured before pitching yeast — a snapshot of total dissolved sugar. Expressed as a number like 1.050, where 1.000 is pure water. Also stated as "gravity points": a 1.050 wort has 50 gravity points. Higher OG means more fermentable sugar and higher potential ABV.
Final Gravity (FG)
The specific gravity of your beer once fermentation is complete — confirmed by two identical readings taken 24–48 hours apart. Always lower than OG, because yeast has converted sugars into alcohol (which is less dense than water) and CO₂ (which leaves the liquid). Typical beer FG ranges from about 1.004 to 1.025.
Specific Gravity (SG)
A dimensionless ratio of a liquid's density to the density of water at 4°C. Pure water = 1.000. Wort at 1.050 is 5% denser than water. A standard homebrew hydrometer measures specific gravity directly and is the most common measurement tool for homebrewers.
Alcohol by Volume (ABV)
The percentage of the finished liquid's volume that is ethanol. The standard measure for alcohol content on commercial labels worldwide. Calculated from gravity drop: ABV = (OG − FG) × 131.25. A 5.25% ABV beer means 5.25 mL of pure ethanol in every 100 mL of beer.
Alcohol by Weight (ABW)
The percentage of the finished liquid's mass that is ethanol. Always lower than ABV because ethanol (density ≈ 0.789 g/mL) is lighter than water. ABW = ABV × 0.79336. Some U.S. states historically required or allowed ABW labeling; ABV is the global standard. To convert ABW back to ABV: ABV = ABW ÷ 0.79336.
Apparent Attenuation
The percentage of original fermentable potential the yeast has converted, calculated as (OG − FG) ÷ (OG − 1) × 100. "Apparent" because alcohol's lower density makes the hydrometer read slightly lower than the true residual sugar level, overstating how much was fermented. Typical range: 70–85% for most ale and lager strains. High attenuation = drier, lower-FG beer.
Hydrometer
A sealed glass instrument that floats in liquid and reads specific gravity from a graduated scale. It works by Archimedes' principle: denser liquids float it higher. Homebrew hydrometers are calibrated for a specific temperature (usually 60°F or 68°F) — measuring at a different temperature requires a correction. Used for both OG and FG; the correct instrument to use for FG on finished beer.
Refractometer
An optical instrument that measures sugar concentration by how light bends (refracts) through a small sample. Fast and convenient for OG readings during or just after the boil — drop in a few mL and read instantly. Not reliable for FG on fermented beer without applying an alcohol correction formula, because ethanol changes the refractive index independently of sugar content.
Temperature Correction
A small adjustment applied to hydrometer readings taken at temperatures other than the instrument's calibration point. A common rule of thumb: add 0.001 SG for every 9°F (5°C) above the calibration temperature. At 80°F on a 60°F-calibrated hydrometer, add 0.002 to the reading. The effect is small for most homebrew but meaningful when precision matters.
Gravity Points
A shorthand for specific gravity that drops the leading "1.0" — so 1.050 becomes "50 points" and 1.010 becomes "10 points." Widely used in homebrew recipes and discussions because the arithmetic is easier: "fermented from 50 to 10 points" means a drop of 40 points, which equals 0.040 × 131.25 = 5.25% ABV (since 40 points = 0.040 SG drop).
Frequently asked
The standard homebrewing formula is ABV (%) = (OG − FG) × 131.25. So if your original gravity is 1.050 and your final gravity is 1.010, ABV = (1.050 − 1.010) × 131.25 = 0.040 × 131.25 = 5.25%. The constant 131.25 is a rounded empirical factor derived from the density relationship between sucrose and ethanol; it gives a close result for most beers in the typical 3–12% ABV range. A more complex formula adjusts slightly for higher-gravity beers, but the difference is generally under 0.2% ABV for most homebrew, making the simpler version the practical standard.
Apparent attenuation is the percentage of original fermentable sugars your yeast consumed: (OG − FG) ÷ (OG − 1) × 100. For OG 1.050 / FG 1.010, attenuation = 0.040 ÷ 0.050 × 100 = 80%. It is "apparent" because alcohol, being less dense than water, makes the hydrometer read lower than the true sugar content — slightly overstating how much was fermented. Attenuation tells you how completely your yeast worked: 70–80% is typical for most ale and lager strains; Belgian strains and highly fermentable worts can exceed 85%. A stuck fermentation shows up as lower-than-expected attenuation relative to the yeast strain's published range.
ABW (alcohol by weight) expresses alcohol content as a percentage of the liquid's total mass rather than its volume. Because ethanol (density ≈ 0.789 g/mL) is lighter than water, ABW is always lower than ABV for the same beer. The conversion is: ABW = ABV × 0.79336. For a 5.25% ABV beer, ABW ≈ 4.17%. ABW appears on some U.S. state labels and in older brewing literature, but ABV is the global standard for consumer labeling. To convert ABW back to ABV, divide by 0.79336.
Most homebrew hydrometers are calibrated to read specific gravity from roughly 0.990 to 1.170, more than covering the 1.000–1.120 range of nearly all homebrew styles. Two factors most commonly affect accuracy: temperature and CO₂ bubbles. Hydrometers are calibrated at a reference temperature (usually 60°F/15.6°C or 68°F/20°C); measuring warm wort makes the liquid less dense, causing the hydrometer to read falsely low. Always cool the sample first. Also, CO₂ bubbles clinging to the instrument inflate the reading — spin the hydrometer gently and read from the bottom of the meniscus at eye level.
Final gravity is stable — and fermentation is complete — when you get the same hydrometer reading two days in a row. A single low reading is not confirmation; residual CO₂ off-gassing and minor temperature swings can mimic gravity movement. Most ales reach a stable FG within 7–14 days at proper fermentation temperature. Lagers fermented cold can take 3–6 weeks. Signs of a stuck fermentation include unusual sweetness, lower-than-expected attenuation for your yeast strain, and a reading that hasn't moved in several days. Rousing the yeast, raising temperature slightly, or repitching a fresh starter are common remedies.
Refractometers are calibrated for pure sugar solutions. Once alcohol is present in your fermented beer, the alcohol bends light differently than sugar does, causing the refractometer to read a falsely high final gravity. To use a refractometer for FG, you need a correction formula (commonly the Novotný equation) that adjusts for alcohol content — most homebrew apps include this. Most homebrewers simply use a hydrometer for FG readings, which is not affected by alcohol, and reserve the refractometer for quick OG checks during and just after the boil. This calculator assumes both OG and FG are standard hydrometer readings in specific gravity.
ABV is determined by how many gravity points were fermented, not by OG alone. A beer starting at 1.080 that finishes at 1.020 (60 gravity points converted) yields ABV = 0.060 × 131.25 = 7.88%. A beer starting at 1.050 that finishes at 1.008 (42 points) yields ABV = 0.042 × 131.25 = 5.51% — lower ABV despite a lower FG, because it started lower. Boosting ABV means increasing OG (more fermentable sugar), achieving a lower FG (more complete fermentation), or both. Adding simple sugars like dextrose raises OG and is highly fermentable, pushing FG down and ABV up. Malt-heavy worts with more unfermentable dextrins leave a higher FG and lower ABV relative to their OG.
For homebrewing purposes — sharing with friends, keeping batch records, understanding your beer — yes, the formula is accurate to within roughly ±0.2–0.3% ABV for typical beer gravities. The sources of error are your hydrometer measurement precision (a reading to the nearest 0.001 is common; 0.002 off on FG changes ABV by about 0.26%), temperature correction accuracy, and the slight approximation in the 131.25 constant. For commercial or legal labeling in jurisdictions that regulate ABV, certified laboratory analysis is required — a homebrew hydrometer is not sufficient for legal compliance. This calculator is for educational and homebrew planning purposes only.
Common mistakes with the ABV calculator
The formula is simple — the inputs aren't. These are the errors that cause real homebrewers to get ABV numbers that are off by more than a few tenths.
Using a warm sample without temperature-correcting the hydrometer
Most hydrometers are calibrated at 60 °F (15.6 °C). Measuring wort at 80 °F makes the hydrometer read roughly 0.002 SG points low — shifting final ABV by about 0.25%. That compounds across both the OG and FG readings. Cool the sample to near your hydrometer's calibration temperature before measuring, or apply a temperature correction table.
Using a refractometer for final gravity without alcohol correction
Refractometers are accurate for OG (no alcohol present yet). Once fermentation starts, ethanol bends light differently than sugar, causing the refractometer to overstate remaining Brix and therefore overstate FG. An uncorrected refractometer FG fed into this calculator will underreport ABV — sometimes by half a percent or more. Use a hydrometer for FG, or apply the Novotný correction formula.
Treating a single FG reading as final
One low reading does not confirm fermentation is complete — CO₂ off-gassing and temperature swings can mimic gravity movement. If you bottle or plug in a "final" gravity that is actually 0.004–0.006 SG above true final, your ABV estimate will read lower than the beer you actually bottled. Confirm FG with two identical readings taken 24–48 hours apart.
Reading the hydrometer at the top of the meniscus instead of the bottom
The liquid curves upward where it meets the glass. The correct reading is at the bottom of that curve, with your eye level with the liquid surface. Reading at the top of the meniscus inflates the SG reading by 0.001–0.002 points — a 0.1–0.25% ABV error on every measurement.