IBU Calculator
The IBU Calculator will use your recipes pre-boil and target batch size to calculate your beers estimated bitterness rating (IBU).
All of the calculations have been adjusted for full & partial mash batches and will also take into account the average utilization differences between whole leaf hops and pellet hops.
IBU Chart by Beer Style located below.
**The general consensus is that full batch recipes will get a more accurate number by using Tinseth’s formula, while Rager’s tends to be more accurate for partial boils. That said, IBU calculation is not an exact science, there are simply too many variables to account for. The truth is we still don’t know what drives hop utilization! For what it’s worth though, I personally prefer taking the average from all of the above formulas.
About the IBU Calculator
Depending on the formula, hop utilization will be adjusted 10% up or down based on the type of hops you are using (Whole leaf Vs Pellet) and Estimated Boil gravity will be substituted in place of Original Gravity in the above calculator to compensate for adjustments in Partial + Full Mash pre-boil volumes and water additions.
So for example, if you are using a partial mash formula, you would enter something like 3 gallons for the pre-boil volume and 5 gallons for the target batch volume. The formula used to calculate this Estimated Boil Gravity is as follows:
((final volume x (final gravity – 1)) / estimated boil volume) + 1 = estimated boil gravity
Finally, The IBU calculator then uses the information you’ve supplied about your hop additions and finds your average IBU rating by combining the results from 4 of the most popular IBU formula’s.
Average IBU’s = (Tinseth + Rager + Garetz + Daniels) / 4
Below you will find a detailed break down of each of the formula’s used in this calculator, along with some real word examples.
Tinseth’s IBU Formula
IBUs = decimal alpha acid utilization * mg/l of added alpha acids
Tenseth’s base formula is simple enough, We just need to solve for our mg/l of alpha acids and decimal alpha acid utilization% to find our brews estimated IBU.
mg/l of added alpha acids = (decimal AA rating * ozs hops * 7490) / gallons of wort
Decimal Alpha Acid Utilization = Bigness Factor * Boil Time Factor
Bigness factor = 1.65 * 0.000125^(wort gravity – 1)
Boil Time factor = (1 – e^(-0.04 * time in mins) )/4.15
**Note: e = 2.71828
Tenseth’s Formula Example
Batch Information
Pre-Boil Volume: 6.5 gallons
Target Batch Size: 5 gallons
Original Gravity: 1.050
Hop Additions
1.5oz Hops – 6.4% AA @ 45 mins
1 oz Hops – 5% AA @ 15 mins
The nice thing about Tenseth’s formula is that it can easily be broken down into smaller components. We just have to solve the foundation equations, then we can plug in our variables to find our IBU for the example beer recipe above.
mg/l of added alpha acids:
(.064 * 1.5oz * 7490) / 5 = 143.808
(.050 * 1oz * 7490) / 5 = 74.9
Next we need to solve for our Decimal Alpha Acid Utilization by solving for our Bigness Factor and Boil Time Factor:
Bigness factor:
1.65 * 0.000125^(1.05- 1) = 1.052
Boil Time factor:
Hop Addition #1: (1 – 2.71828^(-0.04 * 45))/4.15 = .201
Hop Addition #2: (1 – 2.71828^(-0.04 * 15))/4.15 = .108
Now we can go ahead and solve for Utilization % for our hop additions.
Hop Addition #1:1.052 * .201 = .211
Hop Addition #2:1.052 * .108 = .113
IBUs = decimal alpha acid utilization * mg/l of added alpha acids
Hop Addition #1: .211 * 143.808 = 30.34 IBU’s
Hop Addition #2: .108 * 74.9 = 8.08 IBUs
30.34+8.08=38.42 Total IBUs
**Remember your order of operations!
Parenthesis > Exponent >Multiplication >Division > Addition > Subtraction
Rager IBU Formula
IBU = (OUNCES OF HOPS * %UTILIZATION * %ALPHA * 7462) / (Batch Volume* (1 + GA))
Ragers formula uses the Gravity Adjustment factor (GA) to compensate for batches of higher gravity. (anything over 1.050) So If Boil Gravity is less than 1.050 GA = 0.
otherwise,
GA = (BOIL_GRAVITY – 1.050) / 0.2
%UTILIZATION = 18.11 + (13.86 * hyptan[(MINUTES – 31.32) / 18.27] )
Rager’s Formula Example
Batch Information
Pre-Boil Volume: 6.5 gallons
Target Batch Size: 5 gallons
Original Gravity: 1.050
Hop Additions
1.5oz Hops – 6.4% AA @ 45 mins
1 oz Hops – 5% AA @ 15 mins
Using are example batch information from above, We already know that because our Original Gravity value is not GREATER than 1.050, our Gravity adjustment factor will equal 0.
Now let’s find our Utilization factor:
Hop Addition #1: 18.11 + (13.86 * hyptan[(45 – 31.32) / 18.27] ) = 26.90%
Hop Addition #2: 18.11 + (13.86 * hyptan[(15 – 31.32) / 18.27] ) = 8.22%
Lastly, Know that we know our Utilization factors and our GA value, we can solve for IBUs.
Hop Addition #1: (1.5oz * .2690 * .064 * 7462) / (5* (1 + 0)) = 38.54 IBUs
Hop Addition #2: (1oz * .0822 * .050 * 7462) / (5* (1 + 0)) = 6.13 IBUs
Total IBUs = 38.54 + 6.13 = 44.67 Total IBUs
Garetz IBU Formula
According to Garetz, There are several ‘combined adjustements’ (CA) required to calculate a beers IBU rating more accurately. Where GF is Gravity Factor, HF stands for the hopping factor and TF stands for temperature factor.
In the calculator above we use a similar formula to calculate for estimated Boil Gravity. Garetz is essentially doing the same thing here by first finding the ‘concentration factor’ (CF) and then the Boil Gravity(BG) value.
IBU = (%Utilization * %Alpha * Hop weight(oz) * 0.749) / (Volume in gallons * CA)