I think I'll experiment a bit as someone suggested
I need to get used to my new burner and 40 quart pot anyway
I know some people use calculators and I saw this one referenced online
http://www.brew365.com/mash_sparge_water_calculator.php
But I think it assumes there is a sparge and it's not necessarily specific for BIAB at full volume
But I plugged in numbers anyway
Variables
Batch size 5.5
Grain bill 10.25
Boil time 1
Trub loss 0.5 gallon
Equipment loss 1 gallon (default)
Mash thickness 1.33 quarts (default)
Grain temp 70 (default)
Target mash temp 152
Constants
Wort shrinkage 4% (default)
Grain absorption 0.08 (default was 0.13)
Percent boiloff per hour 10
Results
Total water needed 8.76 gallon
Mash water needed 3.41 galloon
Sparge water needed 5.36 gallon
Strike temperature 164.3
Pre boil wort produced 6.94 gallon
So if I'm aiming for 5.5 gallons of wort at the end, I'm assuming if I don't sparge, I just go with around 8.76 gallons for full volume boils
I know this isn't an exact science and there's a fair amount of experimentation, but this looks like a good ballpark figure to start with, unless you guys think that some of the variables are too high
If there is a better BIAB full volume calculator, that seems to be more accurate in your experience, can you point me to a link