Add up the sides.
width*height*length=perimeter of a rectangular prism! :)
There is no way to find perimeter from a 3D figure. However, you can find the perimeter of a side of a triangular prism by using perimeter formulas for a parallelogram or triangle.
Okay, the last person who edited this, totally screwed up. The formula to find the surface area of a square prism is 2B+Ph, multiply the length of the width of the base to get the area, then multiply that by two. After you have multiplied the base twice, et the perimeter of the base and multiply it by the height of the square prism.
It is the perimeter of a triangle times the length of the prism (in square units).
The same way you find the perimeter of a rectangle, add the side lengths
You look at the edge of the triangular prism and count the points
1/2 AP where A=apothem and P= perimeter
Side1 + Side2 + Side3
It is p*h square units.
find the perimeter of a square that has 12 m side
Divide the perimeter by 4 and then square the result to find the area of the square.
12 the base times the height