The name for a geometric diamond shape is a rhombus. A rhombus is a four-sided figure with all sides measuring the same length, but, unlike a square, all angles are not 90 degrees.
Any side of the rhombus potentially serves as its base. The formula for finding the perimeter of a rhombus is identical to the formula for the perimeter of a square: four times the length of one side. Finding the area requires also finding the height of the rhombus. The height is the measurement of a perpendicular line drawn from the base to the opposite side. The opposite side sometimes has to be extended for the line to be perpendicular. Multiplying the height times the base yields the area.