Let the side of the smallest triangle be 1 unit, then: number of the smallest triangle (with side 1 unit) = 12 number of triangles with side 2 units = 7 number of triangles with side 3 units = 3 number of triangles with side 4 units = 1 Total number of triangles in given grid = 12 + 7 + 3 + 1 =23