Need the formula for the surface area of a triangular prisim? Hi, The surface of a triangular prism is composed of three rectangles and two triangles. To find the surface area of the prism add the areas of the five pieces. To find the areas of the triangular pieces you can use the fact that the area of a triangle is onehalf of the base times the height. If you don't know the height but you know the lengths of the three sides of a triangle you can find its area using Heron's formula. Cheers,Penny
