First whole grain batch!!!

We are looking to make 15 gal. of Oatmeal Stout. We have 33 lbs. of grain and want to end up with 11 gal of wort. How much water do I need to steep and sparge?

Oh man... you should really read up on here about "mashing" before you go for this. That's a huge batch of beer, way to much to waste with noobie mistakes. You will need about 12 gallons of water to mash, and 9 gallons to sparge. What are you mashing in, a bathtub? Also, how is it that you are making a 15 gallon batch of beer with 11 gallons of wort?

I have a 50 gal mash-ton, but of course I will not be using all of it. (it is a upright cylinder) And as for the 15 gal finished quantity I only have the ability to boil 15 gals so I want to leave some room to reduce any boil over but will top off the fermenter to 15 gals with sterile water at the end. (The recipe has been made to compensate the toping off. A friend who teaches whole grain brewing helped me come up with the recipe.) I am just not sure about my water quantities, and wanted a second opinion.

Thank you bottle bomber for the reply. Everything went great! I have ~14gals of oatmeal stout bubbling like crazy in the basement.

Nice!