Make sure to slice the steaks against the grain after resting for maximum tenderness. To find the grain, simply look at the surface of the sirloin and notice how the fibers are running parallel in one direction. You want to cut across the grain, perpendicular to the fibers. This will allow the strands or fibers to be much shorter in each slice, and much easier to chew. You can slice sirloin steak as thin as ¼-inch thick, or slice thicker slices, up to 1 inch.