how much pea gravle will it take to cover and area that is 350 sq ft, going 3inch deep??

Answer 1

can't work feet and inches so change inches to feet = 0.25' = 3"---350 sq. ft x 0.25' = 8750 cu. ft.
One cu. yd = 27 cu. ft. therefore 8750 divided by 27 = 3.24 cu. yd or 3 1/4 yards as it's called. I would order 3 1/2 to be safe.

Answer 2

Since there are 12 inches in a foot and 12/3 = 4, divide the area you plan to cover by 4 to get the required cubic feet of gravel.

350/4 = 87.5 cubic feet