A two-dimensional diamond shape is also known as a rhombus. A rhombus is akin to a square in that it has four sides with the same length, but unlike those of a square, the sides of a rhombus do not have to intersect at 90-degree angles. The perimeter of any enclosed two-dimensional object is the distance around its exterior. Calculating the perimeter of a rhombus or diamond is simple because of its equal-length sides.

Find the length of one of the diamond's sides. For this example, the length is 45.

Multiply the length by 4 to calculate the diamond's perimeter. For this example, 45 times 4 is 180.

Add each side together to check your answer. For this example, 45 added to itself four times equals 180.