Angular field of view for mirrors

How is it possible to calculate field of view in degrees for flat and convex mirrors? I have 3D interior car mirror models with dimensions in CAD and I have to figure out if my convex car mirror has 180° field of view. Also I have to figure out field of view for flat car mirror in degrees. Is there any formula or calculation particularly for angular field of view of a mirror? I searched long time on the internet, but it does not give much information about FOV in degrees. If the location between a mirror and an object is necessary, then that is a car interior mirror so there is a small distance.