This fan covers fits all standard size ventilation fans. The finished dimensions are approximately 16.5" x 16.5". Stelletek fan covers are constructed with an exterior side of black waterproof fabric, interior insulating layers of reflectix and polartec and a fabric of your choice facing the interior. The Stelletek fan cover is held in place magnetically to magnetic strips (included) that are installed on the underside of the plastic fan cover. Beautiful and functional! *Fan cover can be folded halfway open and remain in place.