We typically use the 1/2 size steam table pans from Sam's. They hold 1 gallon when level full. I tested that theory with a gallon jug when I first started out so that I could do the math properly. There are 128 fluid ounces in a gallon. If you start with a full pan and do 4oz servings you will get 32. If you start 3/4 full and do 8oz servings you will get 12. For planning purposes I go with a 1/2 pan per 25 people. Some take more than 4 oz and some take none at all when going through the line so it averages out. That rule of thumb has worked out well for me.
Brian Sweeney - CBJ #3691 - '77 Step Van Mobile Kitchen, Horizon Marshall, WSM with Pro Q Stacker, Weber Kettle & Smokey Joe GOLD.
"Any sufficiently advanced technology is indistinguishable from magic" - Clarke's Third Law