about 18 cubic feet.
That's not enough information. You need to know the width of the trench, and how much volume 1 ton of gravel is equivalent to.
about 71 cubic metres of gravel i think
It depends how deep you want the gravel to cover, if you want it to be 2 inches deep it's going to cost more than 5 inches. Also it depends how big the gravel is cut, I think that the smaller the gravel is the more it costs.
Based on sand and gravel calculator found on L.R. Faulk Construction Co. site, 1 ton of gravel (clean rock) will equal approximately 7.3 sq. ft x 6 inches deep, or 5.2 sq. ft x 3 inches deep. A ton of gravel will cover approximately 15 square yards (135 square feet) at 3 inches deep.
You'll need about 28.704 cubic yards (37 tons) of gravel.
Plan on about 2.2 cubic yards (2.8 tons) of gravel.
You will need about 463 cubic yards (around 594 tons) of gravel for this area.
13 1/4
16.36 cubic yards.
5.16 yd^3 (when they say a "yard" of gravel, they mean a cubic yard).
Depends on what depth you want to spread the gravel at. This answer depends on knowing the cubic capacity of 50 lbs. of gravel.
A rectangle area that is 12 feet by 14 feet by 6 inches deep is equal to 3.11 cubic yards. This job would require 4.2 tons of gravel.