Hops correcting for recipes

[kmonty]

I made a Blonde Ale using the recipe from the Brewing Classic Styles book. I put all the ingredients into Beercalculus.com and noticed the IBU's ended up being around 14, when the recipe called for a little over 20. I noticed this after returning home from the brew store and went ahead anyway. Not surprisingly, the beer could use a bit more bittering.

With the alpha acid number changing on hops, how do you compensate for it when you only find out when buying the ingredients? I want to avoid standing, staring at the fridge with hops in it, trying to do some calculation in my head.

Hope this makes sense.
Thanks!

 

[NyPDFustercluck]

Use the calculator on your phone. Just take the aa% X the grams of hops to be used. That's your base "bittering level" once you have that #, you can just divide it by the aa% of the hops available, and presto, in under a minute you've got your required weight.

 

[kmonty]

Thanks! That will come in very handy while at the brew store!