Are you batch of fly sparging? Just curious.
I built a very basic spreadsheet with which to log my brews, and the most useful aspect of that sheet is a 'water needed' section.
Water Needed | Wort Recovered
7.8 pounds grain |
=A2*1.25 quarts | Circumference Depth
=A3/4 gallons | 14.5 5.5
| Cubic Inches _> =PI()*(D4/2)^2*E4 =D5/231
The above are my formulas, set for 1.25 qts/ lb. Basically, input pounds of grain and it spits out gallons required. The stuff on the right is a simply volume recovered table using cylinder volume (pi*r^2*h) for my 14" diameter kettle.
BeerSmith will do the water needed calculation much more sveltly but I find it nice to double-log everything with Excel. Plus I don't have to search through menus looking for the proper tool.