How much do I reduce the bittering hops for full boil?

I'm doing a cream ale kit for my first home brew. The directions are for a partial boil but I plan to do a full boil. I plugged the recipe in the hopville beer calculus program and to get the same IBUs it appears I need to reduce the bittering hops (1 oz Williamette 4.7 AAU) by 40%. Based on searches I did on this site, that seemed a little higher than usual. Now, I'm not sure how great this program is or if I made an error myself. The FG in the hopville program matched the directions, but the OG it calculated was higher than intended (1.063 versus 1.052), so I may have made an error somewhere when I entered the data. Thanks for your help.

I have the 200 commercial beer clone book and the authors say to reduce the hops by 23% when performing a full boil.

Brewing software can vary depending on how the recipe was calculated. A lot of times when I put a recipe into Beersmith the OG and FG estimations differ a bit, although an 11 point OG difference does seem like a lot.

A 40% difference in bittering hops seems huge. Are you sure you're adjusting the recipe correctly? If there are other hop additions besides the bittering hops, you need to adjust those as well.

There should be a "scale recipe" feature on the program that calculates the differences in every addition as the boil volume changes.

nefarious_1_ said:

Brewing software can vary depending on how the recipe was calculated. A lot of times when I put a recipe into Beersmith the OG and FG estimations differ a bit, although an 11 point OG difference does seem like a lot.

A 40% difference in bittering hops seems huge. Are you sure you're adjusting the recipe correctly? If there are other hop additions besides the bittering hops, you need to adjust those as well.

There should be a "scale recipe" feature on the program that calculates the differences in every addition as the boil volume changes.

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I hope I'm adjusting correctly. This is my first time so I have my doubts considering the OG is so much higher and it calls for a 40% reduction in bittering hops (20-30% seemed to be more normal from searches I've done). The only parts I thought I could have gotten wrong were the malts used - I wasn't 100% sure which 2-Row malt to select - I said American 2-Row (directions and bag of 2-RowI received from don't havy any more info than that it's 2-Row). The other part I wasn't sure I did correct was the process. There was a place that asked for the batch size, and a place that asked for the boil size. Batch size was 5.25. The boil size per instructions was 3 gallons. I adjusted this to 5.25 for the full boil (though I will go at last 1/2 g higher in full boil to account for water loss) and reduced the hops number until the IBUs for each process matched. And yes, there is another hop - 1 oz of Fuggle 4.2% AAU, but this is an aroma hop added for the last 5 minutes, and from what I understand the aroma hops aren't adjusted.