Calculated my Mark II's coal volume capacity for the maximum pounds of coal I could ever use per firing.
Here are the dimensions I got. Width of firebox between tiles = 20.5", Frt to back width between tiles = 10". Vertical depth front (grate to tile top) = 5", Vertical depth rear (grate to tile top) = 9". With the assumption that the coal is banked frt to rear the average coal depth lets say is 7" (5+9/2). So the coal volume that pretty much lies within the tiles is, in sq. in., 20.5 x 10 x 7 = 1435 sq.in. /1728 sq.in/cubic ft = .83 cubic foot of coal . This calculation does not address a mound of coal that could be a little higher in the center of the box.
Harman says the the "firebox" volume is 1.90 cubic feet which seems pretty misleading to me since I was (stupid me) originally assuming you could load 1.90 cubic feet of coal in, which apparently is incorrect though Harman is likely considering the "firebox" as the coal volume plus the space above the coal top and below the baffle to come up with 1.9 cu. ft.
Not a killer here, though the .83 cubic feet tells me a complete reload of coal (not considering the old hot coals that keep the new coal burning) is something like 41-42 lbs of coal (assuming roughly ~50 pounds per cubic foot give or take whether it's pea, nut, etc.)
From here there can be some rough estimates regarding the # of reloads or partial reloads per day and month, ect. though there are of course other variables like a cold or warm winter, if you have a fields draft control, and thats a subject discussed a lot elsewhere.
Just though this max pounds per reload would be interesting for your coal estimating purposes. Similar could be done for the other Mark's, though the above reflects a Mark II. Something to do on a Sunday PM before the rain. See ya.