Calculating IBUs for Hop Bursting

Northern Brewer General
1

I’m planning on making an Imperial Red Pilsner for my next beer. I intend on mixing the following hops (AA%) in one bowl, and then adding them to the schedule as shown. It doesn’t really matter how many IBUs it ends up being, but I was curious if there was a way to calculate the average alpha acid value. I multiplied the amount of each hop * the alpha acid values, and the average came out to 14.5% AA. Is this right?

2.25 oz Czech Saaz @ 3.5%AA
1.50 oz Tettnang @ 4.5%AA
2.75 oz Mt. Hood @ 4.6%AA
2.00 oz Warrior @ 15.4%AA

Schedule:
1.25 oz @ 45
1.00 oz @ 15
1.50 oz @ 10
2.00 oz @ 5
2.75 oz @ 0

In addition, I am First-Wort hopping an oz of Warrior.

2

If you multiply the AA% x the ounces, then divide by the total ounces, you get an average IBU of 6.8.

3

I came up with 6.83% AA

For each variety you would calculate the total AA%:
Amount * AA% = total AA

Once you have the total AA% of each variety, add them together and then divide by the total amount of hops.

total AA/ total weight = AA% per oz.

2.25 oz Czech Saaz @ 3.5%AA = 7.875
1.50 oz Tettnang @ 4.5%AA = 6.75
2.75 oz Mt. Hood @ 4.6%AA = 12.65
2.00 oz Warrior @ 15.4%AA = 30.8

30.8+12.65+6.75+7.875= 58.075

58.075 / 8.5 = 6.83 AA%

4

Crap. Forgot to divide by the total ounces again! Thanks!