Free ABV (Alcohol by Volume) calculator
Turn your two hydrometer readings into a precise alcohol by volume — enter your original and final gravity to see the standard and the more accurate brewing formula, plus apparent attenuation, updated live, as you type.
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For home brewing and winemaking only. Please drink responsibly.
Results are estimates. Consult a professional.
How the ABV calculator works
Alcohol by volume is worked out from two hydrometer readings, not from the alcohol itself. You take the specific gravity of your wort or must before fermentation — the original gravity, or OG — and again once fermentation finishes — the final gravity, or FG. As yeast turns sugar into alcohol the liquid grows less dense, so the drop from OG to FG measures how much sugar fermented, and from that the alcohol.
What the result tells you
The headline number is the alcohol by volume — the percentage of the finished drink that is pure alcohol. The calculator also returns apparent attenuation, which is the share of the original sugar the yeast fermented away. Together they tell you both how strong the batch is and how completely it fermented, which is the first thing to check if a beer finishes sweeter or weaker than the recipe promised.
The two ABV formulas, and when each one wins
Most ABV pages give you one formula and leave it there. This calculator runs both, because they disagree — and the gap is the whole story of why strong beers and wines are easy to mis-measure.
The standard formula: fast and fine for session strength
The simple equation, (OG − FG) × 131.25, treats the gravity drop as a straight line to alcohol. It is accurate to within about ±0.3% for beers up to roughly 1.070 OG, which covers most pale ales, lagers and session beers. Below about 6% ABV the two formulas agree within a tenth of a percent, so for everyday batches the simple number is all you need.
The accurate formula: for big beers, wine and mead
As a wort gets stronger, the alcohol itself changes the density in a way the straight-line formula misses, so the standard equation quietly underestimates. Hall's formula corrects for that non-linear relationship and reads higher for high-gravity styles. For an imperial stout, barleywine, wine or mead, the accurate figure is the honest one — and the difference can be more than a full percent.
A worked example using the ABV calculator
Maya brewed a pale ale. Her hydrometer read OG 1.050 on brew day and FG 1.010 once the airlock went quiet for two days running. She wants the ABV and wants to know how completely it fermented.
Step 1 — Find the gravity drop
Subtract final from original: 1.050 − 1.010 = 0.040, or 40 gravity points. That drop is the fuel for every number that follows.
Step 2 — Apply the standard formula
Multiply the drop by 131.25: 0.040 × 131.25 = 5.25% ABV. For a beer this strength, that figure is reliable.
Step 3 — Apply the accurate formula
Hall's equation: 76.08 × 0.040 ÷ (1.775 − 1.050) = 4.20% alcohol by weight, then × (1.010 ÷ 0.794) = 4.20 × 1.272 = 5.34% ABV. The two formulas land within a tenth here, because the beer is under 6%.
Step 4 — Check the apparent attenuation
Divide the drop by the original points above water: 0.040 ÷ 0.050 = 80% apparent attenuation. Four-fifths of the sugar fermented — a clean, healthy result for an ale.
ABV by gravity: a reference table
If you want a sense of the strength before you reach for the calculator, this table pairs common OG and FG combinations with both formulas. Notice how the standard and accurate columns track each other at the top and pull apart as the gravity climbs.
| OG | FG | Standard ABV | Accurate ABV | Attenuation |
|---|---|---|---|---|
| 1.040 | 1.010 | 3.94% | 3.95% | 75% |
| 1.050 | 1.010 | 5.25% | 5.34% | 80% |
| 1.060 | 1.012 | 6.30% | 6.51% | 80% |
| 1.075 | 1.014 | 8.01% | 8.47% | 81% |
| 1.090 | 1.020 | 9.19% | 9.99% | 78% |
| 1.120 | 1.030 | 11.81% | 13.56% | 75% |
Standard = (OG − FG) × 131.25. Accurate = Hall's formula. Below about 6% the columns nearly match; by barleywine strength the accurate figure is well over a percent higher.
How to take accurate OG and FG readings
Your ABV is only as good as the two numbers you feed it. A hydrometer reading off by a few points at each end can shift the result by half a percent, so the technique matters more than the formula.
Read the bottom of the meniscus
Float the hydrometer in a sample tube, spin it to shake off clinging bubbles, and read where the liquid crosses the scale — at the bottom of the curved surface, the meniscus, not the top. Reading the top can cost you a few points, which feeds straight into a wrong ABV.
Correct for temperature
Hydrometers are calibrated to one temperature, usually 60°F or 68°F. A hot wort reads low and a cold sample reads high, so let the sample reach the calibration temperature or apply a temperature correction before you record the gravity. This single step is the most common reason two brewers get different ABV from the same batch.
Confirm fermentation is finished before the FG
A final gravity is only final when it holds steady. Take the FG, wait two or three days, and take it again — if it has not moved, fermentation is done. If you prefer a refractometer for gravity, remember it reads high once alcohol is present and needs its own correction; many brewers confirm the FG with a hydrometer or pair this with a cooking converter when scaling a recipe up.
Apparent attenuation explained
Attenuation is the percentage of the original sugar the yeast fermented. It is the number that tells you whether a batch finished dry, sweet or stuck — and it travels alongside ABV on every reading.
Most ale yeasts attenuate 70–80%. A reading much below that range, with a high FG, points to a fermentation that stalled — under-pitched yeast, a cold spot, or a wort low in nutrient. A reading near or above 80% means the yeast chewed through the sugars and the beer will taste drier.
ABV ranges for beer, wine, mead and cider
The same OG-and-FG math drives every fermented drink, but the starting gravities differ, so the formula choice matters more for some than others. Wine and mead almost always need the accurate formula; most beer does not.
| Drink | Typical OG | Typical ABV | Formula to trust |
|---|---|---|---|
| Session beer | 1.035–1.045 | 3–4.5% | Standard is fine |
| Standard ale / lager | 1.045–1.060 | 4.5–6% | Standard is fine |
| IPA / strong ale | 1.060–1.075 | 6–8% | Accurate reads higher |
| Imperial stout / barleywine | 1.080–1.120 | 8–13% | Use accurate |
| Cider | 1.045–1.060 | 5–8% | Either, lean accurate |
| Wine / mead | 1.080–1.130 | 10–15% | Use accurate |
Ranges are typical starting points, not limits. For anything above about 6% ABV the accurate formula is the honest number.
Why your ABV looks off
When the number surprises you, the cause is almost always a reading or a temperature, not the formula. Here is where to look first.
- FG higher than expected — fermentation may have stalled. Confirm it is stable over two days, then check pitch rate, temperature and yeast nutrient.
- Two calculators disagree — they are using different formulas. Compare the standard and accurate columns above; the gap is normal and widens with strength.
- Reading drifts batch to batch — you skipped temperature correction. A warm or cold sample shifts the gravity by several points.
- Refractometer FG seems high — alcohol inflates a refractometer's final reading. Apply an alcohol correction or confirm with a hydrometer.
- Negative or zero ABV — the FG is at or above the OG, so no fermentation has registered yet. Re-check which reading is which.
Brewing gravity terms, defined
How accurate is this ABV calculator?
The arithmetic is exact. Both formulas are applied to the gravity readings you enter with no rounding until the result is displayed, so the standard and accurate figures are precisely what the equations give.
The accuracy that matters is in your two readings. A hydrometer off by a couple of points, an uncorrected sample temperature, or an FG taken before fermentation truly finished will each move the ABV more than the choice of formula does. Read the bottom of the meniscus, correct for temperature, and confirm the FG is stable, and the calculator will return a number you can put on the bottle. This tool is for home brewing and winemaking — drink responsibly.
Frequently asked questions about the free ABV (Alcohol by Volume) calculator
About this ABV (Alcohol by Volume) calculator
This ABV calculator runs entirely in your browser. Nothing you type is uploaded or stored — your gravity readings stay on your device, and every figure recomputes the moment you change an input.
It sits with the rest of our brewing and kitchen tools. Browse more in cooking & kitchen calculators, or see the full set on the all calculators page.