First all grain

I'm doing my first all grain tomorrow and trying to see if I got this figured right. I'm going to batch sparge 12 lbs of grain. The recipe calls for about 6 1/2 gallons of pre-boil wort. Here's what I'm not 100% sure on, I would add about 4 1/2 gallons in the first batch, and it would retain about 1 1/4 gallons in the grain. After sparging I would then add 3 1/4 gallons let it sit a bit, then run that off. Is that correct?

im assuming your doing a single step mash...so thats 4 gallons of mash h20(1.33 qt per lbs. x12 lbs.=15.96 qt or 4 gallons) then sparge with another 3.5 to end up with 6.5.

that sounds about right.

You have to plan on some the water being absorbed by the grain. I use .1 per pound. You also may have some deadspace in your cooler which you should account for. It might be worth a test to determine that amount. My cooler has approximately 1 quart.
Here is the way I figured it.
Say you mash at 1.2 quarts per pound. You want half of your boil wort on the first running and the rest on the 2nd.
12*1.2=14.4 qts. (3.6 gallons) minus grain absorbtion which 1.2 gallons. You will then have to add about 1.1 gallons at the end of the rest and drain. 2nd running is to add 3.25 gallons which should give you 6.5 not accounting for deadspace.

First add about 1.25 qts per pound of grain ( about 4 gallons) somewhere around 150-155 degrees F and let this sit for an hour, stiring occasionally. The grain will absorb about 1.25 gallons of this. (That should leave about 2.75 avail for draining.) Add another 1 gallon at about 170 Degrees F and let sit for about 5 min, then drain. Add another 3 gallons at about 170, stir and let sit for five min, then drain. You should get about 6.75 gallons from this.

Try this and see how it goes.

Good Luck

Sean