Surface area of Rectangular pyramid (SA) = lb + l s1 + b s2. 'l' is length, 'b' is width. s1 is the slant length of the triangles with base 'l'. s2 is the slant length of the triangles with base 'b'. Example: Find the surface area of a rectangular based pyramid whose base is 12x8 m and slant heights are 10m and 12 m.