How To Convert Sq Ft To Cu Ft?

4 inches deep x 2.5 feet wide x 40 feet long = cubic feet

I have 2500 square feet of lawn I would like to cover with 2inches of black dirt. How many yards of dirt will I need?

You need another dimension to establish a 3-dimensional measurement such as cubic feet.  If you knew the thickness of the textile, you could determine a volume by multiplying the thickness (converted to units of feet) times the square feet of area.

Or you might have the textile wrapped around an object and that could have a volume.  If you wrap the fabric around a box of say, 4 feet by 4 feet by 2 feet, you would have a volume of 32 cubic feet per box.

Without a third dimension, there is no conversion from area (measured in square feet) to volume (in cubic feet).

532 cubic feet to 10x10 square feet

So 5ft = how many cu ft?

Square feet are units used for the area of a place whereas, cubic feet represent the volume.
The formulas for both are:
Area = Length x Width
Volume = Length x Width x Height/Depth*
Hence, we can also say that
Volume = Area x Height

*Height and Depth may be used as appropriate.

So, to convert an area into a volume, we need to multiply it with the height of the container/hole. Then the units will also convert to cubic feet.
Let's suppose, we have a box with an area of 2.5 feet² and it is 2 feet deep. Hence, to convert the square feet into cubic feet, we will find the volume of the box:

Volume = Area x Depth
Volume = 2.5 feet² x 2 feet
  = 5 feet³

1 cubic foot = 12 x 12 x 12 inches
1 sq foot = 12 x 12 inches

Say you have 40 cu ft coverage from a product. How many sq feet coverage can you expect, if you want the product 1 inch thick.

12 x 12 x 12 inches = 12 layers of 12 x 12

12 x 1 cu ft = 12 sq feet

Does that help?