Beer ABV Calculator

The airlock went quiet, the hydrometer reads 1.010 and you remember writing 1.050 on brew day. What is missing is turning that gap into an alcohol figure, either for the label on your own bottles or just to know what you are drinking. The page has exactly those two fields, OG and FG. With 1.050 and 1.010 the answer is 5.25, shown on screen with the word percent after the number.

The math is the familiar shortcut: OG minus FG, multiplied by 131.25. It behaves well up to around 6 or 7% and drifts high above that, because it assumes a fixed relationship between gravity lost and alcohol produced, which does not hold. On a barley wine going from 1.090 to 1.020, the gap between this formula and the second-order versions passes half a percentage point.

Check temperature before trusting the reading: most hydrometers are calibrated at 20 °C and warm wort reads low. If you use a refractometer, alcohol skews refraction, so a post-fermentation reading needs correcting before it goes in here. And ABV is not attenuation: apparent attenuation is OG minus FG divided by OG minus 1, a separate calculation. It all runs in the browser, updating as you type.