Only you can answer that based on your own setup's mash and brewhouse efficiency. Are you using any type of brewing software currently? What is your average efficiency for BIAB? Mashout or no mashout? What volume do you usually end up with before boiling?
There's a really handy BIAB calculator out there that I recently found that you can input all your numbers into that will help you with volumes. I'll see if I can find it.
thanks for you answer. Actually it will be my first attempt at all grain. I will use a BIAB bag in my coleman cooler for mashing. I was thinking about using the no sparge method. I'v seen a simple rule on the internet. Preboil volume + 12 oz per pound of grain as mash water volume. Then I will pull the bag out off the cooler and squeeze the water out and follow the recipe. Does that sounds ok ?