[scott]

I will be brewing the BCS wheat beer recipe on page 192 tomorrow morning.  This is my first BCS recipe so I'm trying to match it as closely as possible.  But I'm not sure how to calculate how many oz of hops to use.  I'll be doing a partial boil of about 3 gallons (with a late addition of half the wheat extract), transfer most of it, then dilute up to 5.25 gallons.

The recipe calls for Hallertau 4% AA, 60 min, 0.8 oz which will give 13.1 IBU (when following the recipe exactly with a pre-boil volume of 7 gallons at 1.043.  Because I'll be doing a late addition of half the wheat extract I expect that my initial gravity will be about the same.  The hops I have are not 4% they are 3%.  I assume that I should add 1.07 oz (4% x 0.8 oz / 3% = 1.07 oz) if I was doing a full boil, but I'm doing a partial boil.  BCS seems to say that it does not matter that I'm diluting, but that just does not make sense.  Should I double the hop addition?  (I'm not a hop head, and I want to match the recipe as closely as possible.)

What do other partial boil late extract brewers do?  

[rbclay]

I use Beer Alchemy on my Mac as my brewing software. Any brewing software will calculate this for you. Basically you are boiling a smaller volume, but because you are also adding some or most of the extract late in the boil your hop utilization is about the same.
Using a brewing program you can pinpoint how much hops you need based on the boil volume and timing of your extract additions.