Since the length is one foot perzactly, the volume (in cubic feet) is equal to the cross sectional area (pi r^2) of the cylinder . . . in feet.
cross sectional area = circumference^2 / 4pi
they're/4th . . .
(circumference in inches * 0.0235079)^2 (* length in ft) = volume in ft^3
. . . "Sew" they sez.