Originally Posted by pkeeler
There are different IBU calculations for whole hops. I don't know if +10% weight would work for all boil times. But they are utilized less, ounce for ounce, than pellets. So, if you substitute them 1:1 in a recipe, your IBUs will be lower.
Right- but how much lower? In a 40 IBU batch, we're talking about 4 IBUs at most (if 10% is indeed correct for bittering hops). And as you said, maybe not for all boil times because leaf hops do seem to have great flavor and aroma. I'm pretty meticulous with my measuring, but not too worried about this.
When I formulate my recipes, I use the AAU on the hops and call it good. I've done the same recipe with leaf hops and pellet hops, especially during the hop crisis when I was using whatever I could get, and never noticed a difference in the perception of bitterness.