The volume formula for a rectangular (or square) box in cubic feet is height(ft) x width(ft) x length(ft), as seen in the figure below: For example, to fill a box with a width of 3ft and a length of 6ft, to a depth of 1ft, you need to multiply 1ft x 3ft x 6ft = 24ft 3 (cubic feet) of gravel, then multiply that by the density.

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