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# Calculating Final Gravity

## TroubleShooting

Q

Could you give some tips or advice on how to best calculate the final gravity of a beer? I often nail the original gravity (OG) down by knowing my system efficiency, but occasionally I am let down by my final gravity differing from brewing software predictions.

A

Calculating the final gravity of a beer is simply a rough approximation because there are too many things affecting final gravity to produce a very accurate estimate. A common estimate is to multiply your gravity points by 0.25 (1.056 has 56 gravity points so the predicted final gravity (FG) would be 14 points or 1.014). Wort fermentability, wort original gravity (i.e., high gravity worts), yeast strain, wort nutrients, wort aeration, and fermentation temperature can all influence a beer’s final gravity. For many beers, the final gravity is something that is discovered during fermentation.

A batch began as 1.056 wort and ended up as 1.018 beer, and after three gravity checks at 1.018 the beer was bottled. Sounds pretty familiar, right? But 1.018 is still pretty high, and when 18 (FG points) is compared to 56 (OG points) we see that the apparent degree of fermentation (ADF) is 68%. ADF can be calculated by the following equation: