Hey everyone, I'm definitely new to brewing (just started fermenting my second 5-gal batch), and I have a question. My first brew was a Hefeweizen, and I tried to primary in a 5-gallon PET carboy....that ended with krausen and beer all over me and my bathroom floor. When I brewed my second batch, I had about 4 gallons of wort, so instead of topping it off immediately to 5 gallons, I decided to wait 24 hours or so after pitching to let the fermentation settle down. I took an original gravity reading of the 4 gallons without thinking about it (I knew 1.061 seemed high...), but I was wondering how I can determine the actual OG if I had added the 1 gallon of water. I'm a chemical engineering student, so I know that you can't just weight the specific gravities, but if the wort is an ideal solution, you can weight the specific volumes...has anyone run into this before, or should I just stop worrying about it so much and buy a 6 gallon primary for next time?