Estimating FG and ABV/ABW

posted Oct 2, 2012, 11:14 AM by Josh Hartley   [ updated Oct 2, 2012, 11:15 AM ]

by: Ron Unz

In last month's newsletter I discussed how to estimate and measure the gravity of your wort before fermentation. In this newsletter, I will be discussing how to estimate your final gravity (FG), calculate the alcohol by volume (ABV), and alcohol by weight (ABW).

Estimating your FG when formulating recipes is pretty straight forward. Start with your OG value and get the number of gravity points from that value. Say you have a 1.048 wort. You can use the last two numbers and assume you have 48 gravity points. I assume to have 75% attenuation on all of my beers. You could choose anywhere between 70% - 80%. Wort composition and yeast type will effect this value, so I assume 75% for simplicity. So take the 48 gravity points and multiply it times 0.75 to get 36 gravity points. Take the original 48 gravity points and subtract the 36 gravity points. You will have 12 points of left over after fermentation is completed or an estimated FG of 1.012. You can use the equation below if you just want to plug in numbers and don't feel like doing gravity point conversions.

Below is the same example as above but using the equation above.

Now that we have an OG and FG, we can estimate the ABV. The two equations below can be used to calculate ABV. It is important to note that both equations will give similar results, but the second one is more accurate.

Now that you have the ABV, you can multiply this value by 1.25 to get an estimate of the ABW.

The equations given can also be used to calculate the real alcohol content of your beer. Replace the OG and FG values used to construct your recipe with measured values before and after fermentation.

If you have any questions feel free to contact me at ronald dot unz at gmail dot com