Slice the watermelon into large slices about 1 1/2 inches thick (or whatever size best fits your glass). Remove the rind and cut each of the slices into cubes.
Places cubes onto a sheet tray. Wrap the sheet tray in plastic wrap and freeze cubes for a few hours or until completely frozen. If not using them right away, place the frozen cubes into a Ziploc bag for easier storage.