Quick question - volume of grain + water

Hey guys, I'm sure this has been answered before, but I'm wondering if there's a good way to roughly estimate the total volume of the mash (grain and water). I'm planning on brewing this RIS: https://www.homebrewtalk.com/f12/chocolate-espresso-stout-40754/

and probably add 1 lb of 2-row to compensate for my consistently low efficiency - this brings the grain bill to 19 lbs. I haven't used this much grain before, and I'm concerned that even with a relatively low water-grain ratio, my 10 gal rubbermaid might not hold it all. Ideas? A simple yes or no would work, but I'd like to have some kind of estimation equation for future reference.

I can mash about 25 pounds in my 10 gallon round Igloo cooler. Here's a cool calculator: http://www.rackers.org/calcs.shtml

go down about 1/2 way- and use "can I mash it?"

Great! Exactly what I was looking for. Thanks!