The thickness of gravel is a product of the square yardage calculation. Square yardage is the amount of material that is used when it is sold by a supplier. Spreading gravel to a specific depth in your yard will require a predetermined area. To do this you need to take proper measurements and use simple math to calculate the cubic yardage, for the required amount of gravel.
Things You'll Need
 Tape measure

Multiply the width by the length to calculate the square footage. Measure the width and length of your yard where you want the gravel. Make a note of the square footage, such as 100 sq ft.

Determine the depth or thickness that you want the gravel, such as 4 inches.

Divide 4 by 12 to calculate the amount of feet for four inches. The result is .333 feet.

Multiply .333 by the square footage that you calculated in step 1, which is .333*100 for a result of 33.3 cubic feet.

Calculate the cubic yardage of gravel by dividing 33.3 by 27 for a result of 1.23 cubic yards.

Divide 33.3 cubic feet by 100 for a result of .333 cubic feet. This is the amount of gravel that covers 1 square foot.

Divide 27 by .333 to calculate the cubic foot amount for 1 square yard, which is 81. This means that an area the measures 9 foot by 9 foot can be covered with 4 inches of gravel.
Tips & Warnings
 Add 10 percent to the total cubic yard amount of gravel that is spread in your yard to allow for settling.
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References
 Big Book of Home HowTo; Better Homes and Gardens; 2003
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