Abstract: This invention relates to rockers for mounting on the legs of chairs to convert the chairs to rocking chairs. The rockers are adaptable to be mounted on chairs having different spacings between the legs thereof, and to be mounted on chairs the bottoms of whose legs are connected by bars. The rockers are also adapted to be releasably or permanently mounted on the chairs. To fulfill all these functions, the inventive rocker, which consists of an arcuately shaped elongated member, has elongated openings adjacent the front and rear ends and on the top surface thereof. The elongated openings receive the legs of normal chairs. Extending across the width of the rocker, and over the elongated openings, are grooves which can receive the bars of chairs whose legs are connected by bars. As the openings are elongated the rockers can be mounted on chairs with different lengths of spacing between their front and rear legs.