ABV Calculator

This Calculator finds your ABV based of your initial and final gravity readings. Make sure to check out the legend at the bottom of this page for more information about each field and the formula’s driving all of the below calculations. (If you’re into that kind of thing)

About The Calculator


The above calculator uses your own measurements for Original & Final gravity to determine your beers Average Alcohol By Volume. When you are using a hydrometer to take these initial measurements, you are essentially measuring the specific gravity(SG) of your beers density as is relative to water. This works because alcohol is less dense than water; so by measuring the difference in your beers density before it begins fermentation and creates the (less dense) alcohol you can then measure the alcohol change by volume. (yay math!)

Below you’ll find a quick run down on the calculations driving each of the results in the above ABV Calculator.

ABV

Over the years there have been a number of different variations of the ABV formula. Most homebrewers are probably familiar with the simplest form of the equation:

ABV = (og – fg) * 131.25

This above equation is simple enough to remember, jot down and solve on a scrap piece of paper, but it’s not quite as accurate as some of the other ABV formula’s that are out there. If you aren’t too concerned with the exact ABV of your brew the above calculation should suffice just fine in most cases, but for higher ABV brews in particular the following formula should prove a bit more accurate.

ABV =(76.08 * (og-fg) / (1.775-og)) * (fg / 0.794)

Example: Using the default values of our ABV calculator ( 1.075 OG & 1.015 FG ), Solve For ABV.

1.) ABV = (1.075 – 1.015) * 131.25 = 7.88%
2.) ABV = (76.08 * (1.075-1.015) / (1.775-1.075)) * (1.015 / 0.794) = 8.33%

 

Plato Scale Conversion

Here we convert our original gravity and final gravity values into their Plato scale values. The Plato scale values represent the percent by weight of sucrose in a given solution, or to put it more simply a 1% Sucrose solution is equivilent to a 1 °P value.

°P = (-463.37) + (668.72 × SG) – (205.35 × SG2)

Example: Using our original values for OG and FG we can use the above formula to find our initial °P and Final °P values.

°P[initial] = (-463.37) + (668.72 × 1.075) – (205.35 × 1.0752) = 18.20 °P
°P[final]  = (-463.37) + (668.72 × 1.015) – (205.35 × 1.0152) = 3.82 °P

 

Real Extract

Real Extract is a measurement of the sugars that are/have been fermented. The value of RE represents the density lowering effects of sugars during fermentation to alcohol.

RE = (0.1808 × °Pi) + (0.8192 × °Pf)

Example: The original gravity of our example wort is 1.075 and the final gravity measurement is 1.015 – What is RE?

RE= (0.1808 x 18.196) + (0.8192 x 3.824 ) = 6.423°P

 

Attenuation

The attenuation values shown in the ABV calculator represent the degree to which the sugar content of your beer has been fermented into alcohol. There are 2 Attenuation calculations used above:

Apparent Attenuation(AA) is an approximate value of the sugars consumed during the fermentation process.

AA = 1 – [°Pf / °Pi]

While Real Attenuation(RA) is calculated using our “Real Extract” value from our previous calculation above, giving us a more accurate number to work with.

RA = 1 – [RE / °Pi]

Example: Using the Initial (18.20°P) and Final ( 3.82°P) Plato values and the Real Extract value (6.42°P) of our example beer, Find AA and RA.

AA = 1 – [ 3.82 / 18.20 ] = .790
RA = 1 – [ 6.42 / 18.20 ] = .647

 

ABW

Once we’ve determined our ABV value of the beer, It’s fairly simple to extract our ABW percent.

ABW = (0.79 × ABV) / FG

Example: Using the ABV value we got in an earlier calculation (7.88%) and the Final gravity value measurement in  our example – Find the beers ABW.

ABW = (0.79 x 7.88 ) / 1.015 = 6.14%

 

Calories

The below equation is essentially comprised of 3 unique formulas that when combined will give us the total estimated calorie content of our beer! The first section in brackets calculates the known caloric contribution of ethanol using our ABW value, the second utilizes the known caloric contributions of carbohydrates. Finally the calculated value is converted from the known caloric value per 100 ml of beer to the much more familiar standard of 12 ounces.

cal per 12 oz beer = [(6.9 × ABW) + 4.0 × (RE – 0.1)] × FG × 3.55

Example: Using all of the previous calculations and their values – Determine the estimated calorie content of our example beer.

~Calories = [(6.9 × 6.14) + 4.0 × (6.423 – 0.1)] × 1.015 × 3.55 = 243.845

 

Rather work offline? You can download the excel version of this Calculator HERE.

References

For an even better in depth analysis of the formulas driving the calculator on this page, Check out the link below.

Straight 2 The Pint