Using 2 cubic foot bags:

One 2 cubic foot bag covers…

DEPTH Area Covered:
8’x8′ (64 sq. ft.)
Area Covered:
25’x4′ (100 sq. ft.)
Area Covered:
12’x12′ (144 sq. ft.)
2″ = 12 sq. ft. 5.3 bags needed 8.3 bags needed 12 bags needed
3″ = 8 sq. ft. 8 bags needed 12.5 bags needed 18 bags needed
4″ = 6 sq. ft. 10.6 bags needed 16.6 bags needed 24 bags needed