ABV Calculator
Two hydrometer readings are all you need to know how strong your brew turned out. Enter the original gravity before fermentation and the final gravity after, and get estimated alcohol by volume, apparent attenuation, and alcohol by weight.
Use temperature-corrected readings for the best estimate — the hydrometer correction calculator handles that if your samples were warm.
Formula & how it works
The headline figure uses the standard estimate ABV = (OG − FG) × 131.25. The advanced figure uses ABV = 76.08 × (OG − FG) ÷ (1.775 − OG) × (FG ÷ 0.794), which tracks density changes better at higher gravities.
Apparent attenuation is (OG − FG) ÷ (OG − 1) × 100, and alcohol by weight is roughly ABV × 0.794.
Worked example
An original gravity of 1.050 finishing at 1.010 gives (1.050 − 1.010) × 131.25 = 5.25% ABV by the simple formula, or about 5.34% by the advanced one. The apparent attenuation is (0.040 ÷ 0.050) × 100 = 80%, and alcohol by weight is about 4.2%.
Reading gravity well
Correct for temperature first
Hydrometers are calibrated to read true at one temperature, usually 60 °F. A warm sample reads low and a cold one reads high, which throws off both gravity points and therefore the ABV. If your samples were not near the calibration temperature, correct them before entering the numbers here.
Simple versus advanced
For everyday session and standard-strength beers the simple formula is perfectly good and is what most brewers quote. As gravity climbs into big stouts, barleywines, and wines, the linear estimate drifts a little low, and the advanced formula's density correction brings it back closer to reality. Both are shown so you can see the gap.
What attenuation tells you
Attenuation is a quick health check on fermentation. A number far below your yeast's expected range can mean a stuck or incomplete fermentation, while a very high one points to a thin, dry finish. Comparing it against the yeast strain's stated attenuation helps you judge whether the beer finished where it should.