Is 40 square feet the same as 40 feet square?

No. They are quite different. They are the same only in the case of one square foot and one foot square. One square foot is a square, one foot on a side. Ten square feet is an area equal to ten of these square feet. Ten feet square is a square, ten feet per side. Ten square feet contains an area of ten square feet. Ten feet square contains an area of 100 square feet.