Brewing Formulas

Here are a few formulas that are going to be useful for finding out some brewing values.


This will show me how much alcohol is in my beer the final reading should be ABV, but you need to know ABW first.

ABW = 76.08(OG-FG)/(1.775-OG)

ABV = ABW (FG/.794)


(Update: an easier method for figuring out alcohol percentage (OG-FG) X 131= AL%)


Here is a formula to figure out OG:


Determining the original gravity is a pretty straightforward process. Multiply the pounds of extract by 38 and then divide by the batch size. As an example, if you're using 6 pound of extract syrup in a 5-gallon batch, your gravity will be 6 x 38 / 5 = 46, or a specific gravity of 1.046.


To figure out the FG :


It's always easier when dealing with gravities to use "gravity points." That's the final two numbers of the hydrometer reading. A 1.052 OG would have 52 gravity points.

In simplest terms, subtract the attenuation percentage from the OG: 52 minus 75% = 13.

To find the attenuation percentage, just multiply the OG (in gravity points) times the expected percentage: 52 x .75 = 39, then just subtract the attenuated portion: 52 minus 39 = 13 or a final gravity of 1.013.

To find your apparent attenuation from your OG and FG numbers subtract the FG from the OG to get the amount attenuated, then divide that number by the OG. So if your OG was 1.052 and your Final Gravity was 1.013: 52 minus 13 = 39. 39 ÷ 52 = 75 or 75% apparent attenuation. A final gravity of 1.015 would be 71% attenuation (52 - 15 = 37; 37 ÷ 52 = 71)