I have been doing a bit of research and just getting confused. I would like to make one which could serve for both 5 and 10 gallon batches. I don't want to get one which could do 10 gal batches only to find that the grain bed is too shallow when doing a 5 gal batch...

John Palmer's site recommends 4" min depth but prefered 8-18" depth. Furthermore :

I dont quite get this. It says to me that 1# of grain volume would be equivalent to 10oz of water volume. So (making the math simple) 10# of grain would have a displacement of 100 oz of water. A 48qt cooler would be 1536 oz (48qt * 32 oz per qt). The grain would occupy 6.5% of the volume (100 / 1536). If the dimensions of the cooler were 9x14 with a depth of 10" then this would have a grain depth of 0.65" (10" * 6.5%) . I know I know... I've got something completely wrong, no way you have just 2/3" of grain bed... what is it? Do the grain swell several times their original size? I don't think this is it with my experience from steeping... I am reading this wrong apparently. Surely the grain takes up more volume than this.John Palmer's site

So, you take your typical batch size (5) and multiply that by your typical OG (1.050) and determine how many pounds of grain that equals, using your typical yield (30) in pts. /lb. /gal. Thus, 5*50=250, and 250/30=8.3 lbs. At a ratio of (2) quarts per pound, the total volume of this mash would be 8.3*(42+32)=616.6 fluid ounces or (dividing by 128) 4.8 gallons. So, I would recommend either the 24 quart rectangular or the 5 gallon cylindrical.

Table 21 - Volume of Unit MashUnits

Volume at Mash Ratio

Volume of Grain Alone

U.S.

@ 1 qt/lb. = 42 fluid oz.

10 fluid oz.

Metric

@ 1l/500g = 1.325 liters

325 milliliters

Well, I've done my homework trying to keep from bothering you with details, but at this point, I need a hand.

I want to use a rectangular (square) cooler since making the drain manifold would be easier (vice a round manifold). The 10gal gott cooler has a surface area of 122 sq. inches. I have found a square cooler with inside surface area of (13x13) 169 sq. inches. This is less than most rectangular coolers (11x18 = 198 sq. inches) . I am hoping that this cooler would give me sufficient grain depth for my 5 gal batch grain bill yet not get too deep for a 10gal batch grain bill. I just can't calculate the grain depths until I get past this hump.

Thanks a TON... I'm really ready to get this done so I can move to my AG!!!