for such a small project I'd forget yards or tons and just get 16.7 cubic feet...for this unless you have a friend with a truck,I'd just buy bags ...less work and cleaner application and probably cheaper than getting a delivery from a pit.
I'm guessing this is a footing for a retaining wall. If so you need to stay a couple of inches below grade so it doesn't show. So the gravel will be a couple of inches less in depth, wright ?
Stone is usually sold by the cubic yard or truck load. So to figure the cubic area you convert it all to inches and then back to cubic yards. (4 x 12) x 50' = cubic area (4 x 12) = 48 X (50' x 12 = 600) = 28,800 cubic inches a cubic yard is (36 x 36)= 1,296 square inches. x 36 = 46,656 cubic inches 28,800 cubic inches divided by 46,656 cubic inches = .617 cubic yards of fill. Not worth a truck
