use the following timings for how long to grill filet mignon by direct grilling: for a 1-inch cut, grill 10 to 12 minutes for medium-rare (145degf) or 12 to 15 minutes for medium (160degf). for a 1 1/2 -inch cut, grill 15 to 19 minutes for medium-rare (145degf) or 18 to 23 minutes for medium (160degf).