Surface area is calculated by adding up all of the areas of the shapes that make up the surface of the object. The formula for calculating surface area differs with the type of object. It is vital to ensure that all units are the same for measuring the areas.
A cube has six squares of equal area, therefore the surface area for a cube is 6 multiplied by A squared. A is the length of each side of the cube.
The formula for a rectangular prism's surface area is 2AB + 2BC + 2AC. A, B, and C are the different lengths of the three sides of the rectangular prism.