How this calculator works
The calculator converts trench width and gravel depth to feet, multiplies by drain length, and converts cubic feet to cubic yards. A waste allowance is applied to the gravel quantity. Fabric area is estimated from trench width plus two side depths plus overlap, multiplied by length. Pipe sections are drain length divided by section length.
Example: an 80 ft drain with a 12 in wide and 18 in deep gravel zone needs about 4.89 cubic yards of gravel with 10% waste, 80 ft of pipe, and roughly 480 square feet of fabric.