The surface area of a rectangular pyramid is found by adding the area of the base to the combined area of the four triangular sides. The area of the base is found by multiplying length times width. The area of each triangle is found by multiplying 1/2 base times height.
A right rectangular pyramid, with the apex direct above the center of the base, has two pairs of congruent triangular sides. In the case of a right square pyramid, all four triangular sides are congruent. The height of a triangular side is not equal to the height of the pyramid, but it can be derived by using the Pythagorean formula.