To calculate the surface area of a rectangular prism, calculate and add together the surface areas of all its faces. Performing this calculation takes just a few minutes.Continue Reading
Measure the lengths of any two edges that come together at one corner. Multiply them together to get the surface area of the face that is common to those two edges.
Measure the length of the third edge coming from that corner, and multiply it by either of the previously measured edges. The answer is the surface area of the face that is common to those two edges.
Multiply the length of the edge measured in the previous step by the length of the edge not used in the previous step. That's the surface area of the face that is common to those two edges.
Calculate the sum the surface areas of those three faces.
Since each of those three faces has a corresponding opposite face of equal area, double the sum to arrive at the final surface area.