Hop reduction in full wort boil - first wort hops?

I'm going to do a full wort boil for the first time using Northern Brewer's Waldo Lake Amber kit.

I ran the IBU calcs through beersmith, and it said to use 18g of the bittering hop addition, and 18g of the FWHs. Both are normally 1oz for a partial boil.

Most of my research here says use 75% of the partial boil amounts, but beersmith says to use only 64% of the hops. Who is right?

75% or 64% is probably splitting hairs with IBU calculations. Really, the accuracy in the IBU calculations is just not that precise. They are good for approximation to style and are useful for trial and error recipe formulation. What I mean by that is that an IBU on your system is going to be different than an IBU on mine or someone else's. You really have to pick a calculation, brew a recipe, see how you like the bitterness, and then increase or reduce your IBU rate until you get it right. While your question is a good one; it just is assuming something about these IBU formulas that their creators will tell you they can't do.

So, use 75% or 64%, doesn't matter, and adjust from there. This is probably why BJCP guidelines have such large IBU ranges for most styles. Aim for the middle.

Experiment and let your taste buds guide you. I use Promash. Early on I decided that I would just pick one of the equations and stick with it. I don't care if the IBU value is accurate. Over time I've calibrated MY taste buds, and I know what MY calculated 20 vs 30 vs 40 IBUs is going to taste like. I use that to guide me in formulating my recipes.

Of course one also has to consider the BU:GU ratio as well (bittering unit to gravity unit). 40 IBUs in a beer with a OG of 1.050 is going to taste different than 40 IBUs in a beer with an OG of 1.080. There are some charts out there to guide us on this according to beer style. That's the beauty of homebrewing, one has to taste a lot of beers, and then brew a lot of beers.

Thanks guys. I guess my scale gives me more accuracy than necessary. The recipe has such good reviews I don't want to mess it up...but after stepping back and thinking about it, I don't know what it'll taste like anyway since it's my first time brewing it. Sometimes I need to reel myself back in, since I'm an Enginerd by day.

I'll shoot for somewhere in the middle and let 'er ride!

William