Portland cement is shipped in 94 pound bags so that it will equal 1 cubic foot by volume.
A five gallon bucket, filled to the top ring(not the brim) is 1 cubic foot of volume.
A concrete block standard nominal size is 8"x8"x16" (Women Have Legs:Width/Height/Length). This is a modular size, based upon the biggest stone a single man could lay by himself(60-70 pounds). The actual face dimensions were based on the golden ratio.
To fill the cores of 4-8x8x16 block requires one cubic foot of material.
A six cubic foot wheelbarrow will only carry 2 cubic feet of concrete.
A cubic yard of sand weighs 2800 pounds, and you, Mr. Homeowner, can NOT carry 2 yards in your Toyota Tacoma.