Properties of regular undecagonsInterior angle147°Like any regular polygon, to find the interior angle we use the formula   (180n–360)/n . For a undecagon, n=11. See Interior Angles of a PolygonExterior Angle33°To find the exterior angle of a regular undecagon, we use the fact that the exterior angle forms a linear pair with the interior angle, so in general it is given by the formula 180-interior angle. See Exterior Angles of a PolygonArea9.365s2
Where S is the length of a side. To find the exact area of a undecagon or any polygon, using various methods, see Area of a Regular Polygonand Area of an Irregular Polygon