IF 6 gallons of grow bed = 1 lb of fish. In optimal theory.

And grow bed is 1/2, 55 gallon drums. 2 ft x 3 ft x 1 ft = 6 cubic ft.
55/2 = 27.5 gallons. 27.5 gallons/6 gallons per 1 lb = 4.58 lbs
Each 1/2 barrel supporting in THEORY 4.58 lbs of fish.

It was easier to convert to gallons than cubic ft. But hopefully someone can follow this and confirm or correct me. Thanks in advance.

I opted not to count gallons of water, as stocking density will effect the concentration of dissolved solids/gallon. So it's inconsistent to count gallons. Add in plumbings, sumps, filters, etc and whatever else and it's not an accurate count anymore.