Quick question for all grain brewers

I am making the transition from extract brewing to all grain brewing. I have participated in brewing a couple of all grain batches with some old friends, but don't remember what Im about to ask. For a 5 gallon batch of beer (lets say the recipe calls for 12lbs of malt), about how much water do you lose during the mashing process? Im sure results differ from person to person, but about how much water is absorbed for you on average?

Grain absorbs .13 gallons of water per pound, and depending on where the drain is on your tun, you could lose anywhere from a quart to a gallon+ of water in the dead space below it.

.12 gal per lb of grain.
.12 x 12 lbs grain x 4 = qts lost.
Don't forget your equipment loss. The water left in the bottom of the tun that you can't get out.

I'll split the difference between the first two answers. Each pound of grain absorbs 1 pint water (so that's 0.125 gallon per pound of grain).
And I agree with both of them that you need to account for the dead space/equipment loss when transferring to the boil kettle.

-a.

Get yourself a copy of ProMash. It makes everything much easier.

This should answer all your questions:
http://www.brewersfriend.com/2010/06/12/water-volume-management-in-all-grain-brewing/