Originally Posted by Yuri_Rage
I used to think that scaling recipes was some kind of cosmic science. In reality, simply multiplying all of the amounts by 3/5 (0.6) will work fine when scaling a 5 gallon batch down to 3 gallons.
This doesn't quite work because you boil off fairly constant amounts of water during your boil. So, your sparge volumes at least tend to be different than just simple scaling.
Regarding Beer Smith, I tend to just rewrite my recipe for the smaller volumes rather than attempting to have Beer Smith scale stuff, because I think there's some kind of bug there where it will scale up OK usually, but scaling down gets wonky, at least in my experience. Also, if I rewrite it I can specify stuff like 1/4 pounds instead of ending up with crap like 0.38 pounds of crystal.