crap I forgot to calculate my pre-boil

I've been doing 7.25 gal for 10 lb grain brew. This time I'm doing 13lbs of grain in my boilermaker 10. I tried a calculator online but it has confusing entries that are perhaps more designed for mash tuns?

Would anyone tell me how much water I need here?

bah even this simple biab calc is punching out numbers that make no sense to me

If you are asking about grain absorption, try using .16 gallons per pound of grain. If 7.25 worked for you for 10lbs, the additional 3 lbs would absorb .16*3 = .48 or about half a gallon additional. So roughly 7.75G instead of 7.25G. Does that sound right?

Grain absorbs approximately 0.1 gallons per pound (depending on the moisture of the grain). So, you will need approximate 0.3 more gallons.

If it were me, i'd aim a little on the high side, if my boil volume was too much, id boil a little longer to compensate.

Another option is using some "top-off" water to get up to your volume. When you are using BIAB, i don't think a 1/4 of a gallon will get you any more/less efficiency when you are boiling it off anyways.

I think I got the number right on the simple calculator. There's just a bunch of other numbers that confused me. It's suggesting 7.61gal. That's probably spot on seeing as I squeeze the crap out of my bag Thanks for holding my hand for a second there