First you need to understand that the "yard" of material is really a cubic yard (3 x 3 x 3) or 27 cubic feet. Each cubic foot is 12 inches by 12 inches by 12 inches.
you begin by multiplying the 15 foot width by the 55 foot length. (15 x 55 = 825) If you assume that you have a 12 inch high fill then all you have to do is divide 825 by 1/4(3 inches) to get the number of cubic feet of top soil. divide again by 27 to get the number of cubic yards.
You would need approximately 2.5 cubic yards of gravel to cover a 12' by 15' area at a depth of 2 inches.
if that is 3 ft deep it would require 96 yards... IF it is 3 inches deep it would require 24 cubic yards
You would need 31.88 cubic yards of topsoil to cover 855 sq feet at 6 inches deep.
That's 13 cubic yards of mulch for every 2 inches deep.
.21 yards of sand will fill an area 115 inches by 67 inches to a depth of 2.5 inches.
You will need about 463 cubic yards (around 594 tons) of gravel for this area.
2.37 cubic yards of stone for every 3 inches deep it needs to be
tweleve
1 cubic yard will cover 15 square yards at 3 inches deep.
You would need about 13 cu yards or about 15 tons.
You would need 3,355 cubic yards of soil to cover 6 acres at 24 inches deep.
105 ft * 84 ft * 3 inches = 105/3 yards * 84/3 yards * 3/36 yards = 35 * 28 / 12 cubic yards = 245 cubic yards.