A kit for converting a standard sit-down desk to a stand-up desk. The kit includes a frame having a plurality of leg extensions secured with end rails and a plurality of side supports of selected length. Selected of the leg extensions are pivotally carried between retracted and extended positions. The kit also includes a foot rail, a shelf, a plurality of spacers and a plurality of collars. For shipping, the pivotable leg extensions, shelf and foot rail are placed parallel with the end rail. In use, the pivotable leg extensions are moved into an extended position and secured by the foot rail and shelf. The desk legs are interconnected with the leg extensions by the collars.