A portable cushion to use with a chair having a seat with upwardly extending elements which may be hip supports or arm rests on each side of the seat having a material thickness sufficient to raise the seating area above the plane of the arm rests or hip supports so as to effectively increase the seating area of the seat. The cushion includes a top wall, a bottom wall, a forward wall, a rearward wall, a first side wall and a second side wall, the respective wall defining a material thickness. The first side wall and the second side wall each have an indentation formed therein to accommodate the upwardly extending arm rest or hip support when the cushion is placed upon the seat of the chair. The material thickness of the cushion is such that the upper wall of the cushion extends at least to the height of the upwardly extending elements thereby effectively creating a wider seat, unencumbered by the upwardly extending elements.