ABV Calculator
Enter your original and final gravity to get alcohol by volume, worked out two ways so you can see how much the choice of formula actually matters for your beer.
- Gravity points dropped
- 40.0
- Apparent attenuation
- 80.0%
- Difference between formulas
- 0.09%
How this was worked out
standard = (1.0500 − 1.0100) × 131.25 = 5.25%
alternate = (76.08 × (1.0500 − 1.0100) ÷ (1.775 − 1.0500)) × (1.0100 ÷ 0.794) = 5.34%
How ABV is worked out from gravity
You never measure alcohol directly at home. You measure density twice — once before fermentation and once after — and infer the alcohol from how far the density fell. Sugar is denser than water, alcohol is lighter than water, so as yeast converts one into the other the reading drops. The size of that drop is the whole basis of the calculation.
The standard formula multiplies the drop by a single fitted constant. That works because across the range most beer occupies, the relationship between gravity lost and alcohol gained is close enough to linear. It stops working at high gravity, where the linear fit drifts, which is why the second formula exists.
Worked example
A beer starts at 1.062 and finishes at 1.012.
Standard: (1.062 − 1.012) × 131.25 = 6.56%
Alternate: (76.08 × 0.050 ÷ (1.775 − 1.062)) × (1.012 ÷ 0.794) = 6.80%
A gap of 0.24 percentage points — small at this strength, and widening as gravity rises.
Common mistake
Taking the final reading with a refractometer. Refractometers are excellent before fermentation and misleading after it, because alcohol changes how the sample bends light. A refractometer FG will read noticeably high and inflate your ABV. Use a hydrometer for the final reading, or apply a dedicated refractometer correction.
Keep going
- ABV and attenuation come from the same two gravity readings; the attenuation calculator turns them into how thoroughly the yeast finished instead of how strong the beer is. Attenuation Calculator
- A refractometer reads Brix, not specific gravity, so a reading has to be converted before it can go into an ABV calculation; the Brix converter does that step. Brix ↔ gravity Calculator
Frequently Asked Questions
Which ABV formula should I use?
For ordinary-strength beer the two barely differ, so the standard formula is fine. The gap opens as gravity climbs: at OG 1.092 and FG 1.021 the standard formula gives 9.32% and the alternate gives 10.17%, nearly a full percent apart. If you brew big beers, prefer the alternate.
Why does the simple formula multiply by 131.25?
It is a fitted constant, not a derivation. Fermentation converts sugar to roughly equal parts alcohol and CO2, and the drop in specific gravity tracks how much sugar went. Multiplying that drop by 131.25 converts gravity points into percent alcohol closely enough for normal strengths, which is why the formula survived from the pre-calculator era.
Can I use a refractometer reading directly?
Not after fermentation has started. A refractometer measures how light bends through the sample, and alcohol bends light differently from sugar, so any reading taken once alcohol is present reads high. Before fermentation it is fine — switch this calculator to Brix and it converts for you.
My FG is higher than my OG. What happened?
Almost always the readings got swapped, or one was taken at a temperature the hydrometer is not calibrated for (most are calibrated at 20 °C / 68 °F). A genuinely rising gravity is physically odd and usually points at a measurement problem rather than the beer.
Does this account for alcohol produced during bottle conditioning?
No. Priming sugar adds a small amount of additional alcohol, typically on the order of 0.2–0.3% for normal carbonation levels. This calculator works from your original and final gravity only, so it reflects the beer at packaging.
Source. Both formulas, and the worked example comparing them at OG 1.092 / FG 1.021, are from Brewer's Friend, Alcohol By Volume Calculator Updated, retrieved 19 September 2026. This is a calculation tool for homebrewing and says nothing about consumption.
Related Calculators
- Brix ↔ gravity Calculator — Gravity & Alcohol
- Attenuation Calculator — Gravity & Alcohol
- Dilution & blending Calculator — Gravity & Alcohol
- IBU Calculator — Hops & Bitterness