That depends upon how thick the foam insulation is. That is the only way to compute from cubic feet to square feet.
To simplify, assume the foam is 1 foot wide by 1 foot thick by 51 feet long. That is 51 cubic feet of foam. If you slice the block lengthwise at 1 inch intervals, you get 12 slices, each 1 foot wide by 51 feet long by 1 inch thick. This is 51 square feet of coverage at 1 inch. You would be able to cover 51x12, or 612 square feet.
Increase the thickness of the slice to 1-1/2 inches, you only get 8 slices, or coverage for 408 square feet.
Any thicker than that, and you won't get enough coverage for 400 square feet.
Answers & Comments
That depends upon how thick the foam insulation is. That is the only way to compute from cubic feet to square feet.
To simplify, assume the foam is 1 foot wide by 1 foot thick by 51 feet long. That is 51 cubic feet of foam. If you slice the block lengthwise at 1 inch intervals, you get 12 slices, each 1 foot wide by 51 feet long by 1 inch thick. This is 51 square feet of coverage at 1 inch. You would be able to cover 51x12, or 612 square feet.
Increase the thickness of the slice to 1-1/2 inches, you only get 8 slices, or coverage for 408 square feet.
Any thicker than that, and you won't get enough coverage for 400 square feet.