# Quick on-the-go IBU calculation

### Help Support Homebrew Talk:

#### Parker36

##### Well-Known Member
Anybody know of a quick formula that you can use to get an approximate IBU value from if you know weight of hops, boil size, and AA%? I know there are tons of online calculators out there, but I want something that I can more or less do in my head when I am at the store.

##### Flyfisherman/brewer
I doubt you would do it in your head unless you can memorize a table of values. You need to know the boil gravity and the utilization factor in order to do the basic calculation.

Palmer has the info on the generic IBU formula.

#### Bokonon

##### Well-Known Member
I'd say figure out a recipe before hand and calculate the AAU (Alpha Acid Units) needed for each addition. Then you can use that to pick of the available hops at the store

#### field

##### Member
I don't know what it's worth, but Brewing Quality Beers by Byron Burch outlines the following simple formula:

IBU = m60 * a60 * 4.0 + m30 * a30 * 1.4 + m15 * a15 * 0.7

where m60 ounces of hops of a60 alpha acid rating are added at 60 minutes, m30 ounces of hops of a30 alpha acid rating are added at 30 minutes, and m15 ounces of hops of a15 alpha acid rating are added at 15 minutes. The thing that Burch points out from this formula is that hops boiled for 60 minutes provide more than twice the bittering effect than the same amount of hops added at 30 minutes.

I recently started a Paulaner hefeweizen clone with 1.0 oz. of Vanguard hops (4.4% AA) that were added at 60 minutes with nothing afterwards, so the formula for me simplifies to:

IBU = 1.0 * 4.4 * 4.0 = 17.6

Note: this formula assumes a 5 gallon batch. Burch writes that if you need a different quantity, divide the final result by (dv/5.0), where dv is the desired volume of your batch. So, if you wanted to do an 8 gallon batch, you'd divide your IBU result by 1.6 to get the true IBU estimate for 8 gallons.

Hope that helps.

#### david_42

##### Well-Known Member
I will make a small assumption here: Your goal is to figure out the weight of the hops you will need, but you don't know the AA% until you get to the store. If that is the case, then plug your numbers into a calculator and use 10% AA for the bittering add. That will give you a weight, W. In the store, the weight of hops you will need is 10*W/AA%.

As an example: beersmith says you need .75 ounces at 10% AA. The store has 8% hops. You'll need 0.75*10/8 or 0.93 ounces.

90% of the time, the IBU contributions from the flavor & aroma hops will be at the noise level.

#### McGarnigle

##### Well-Known Member
Use Palmer's nomograph in How to Brew. It takes up about half a page; bring it wit you and use a credit or library card as a straight edge. Online, this would be the link in bradsul's response above, about 2/3rds of the way down. Not sure how it prints. Palmer also sells a version of it, or someone can just scan and email it to you.