APPENDIX K ITF RULES OF TENNIS APPENDIX IX SUGGESTIONS ON HOW TO MARK OUT A COURT Including Blended Lines Note:  All court measurements shall be made to the outside of the lines. The following procedure is for the usual combined doubles and singles court. (See  note at foot for a court for one purpose only.) First select the position of the net; a straight line 42 feet (12.80 m) long. Mark the  centre (X on the diagram above) and, measuring from there in each direction,  mark:  at 13’6” (4.11 m) the points a, b, where the net crosses the inner sidelines,  at 16’6” (5.03 m) the positions of the singles sticks (n, n),  at 18’0” (5.48 m) the points A, B, where the net crosses the outer sidelines,  at 21’0” (6.40 m) the positions of the net posts (N, N), being the ends of the original  42’0” (12.80 m) line. 473