Rock is normally sold in cubic yard volumes. 1 cubic yard of rock will cover approximately 100 square feet of area at 3" thick.
Depends on how thick you spread it.
A cubic foot of rock is 12 inches by 12 inches by 12 inches. If the rock is spread one inch thick, 12 inches wide, it will cover approximately 12 feet. It really depends on how big of an area you want to cover and what it's purpose will be.
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