A tennis court is the venue where the sport of tennis is played. It is a firm rectangular surface with a low net stretched across the centre. The same surface can be used to play both doubles and singles matches. A variety of surfaces can be used to create a tennis court, each with its own characteristics which affect the playing style of the game. Dimensions The dimensions of a tennis court are defined and regulated by the International Tennis Federation (ITF) governing body and are written down in the annual 'Rules of Tennis' document. The court is long. Its width is for singles matches and for doubles matches. The service line is from the net. Additional clear space around the court is needed in order for players to reach overrun balls for a total of wide and long. A net is stretched across the full width of the court, parallel with the baselines, dividing it into two equal ends. The net is high at the posts, and high in the center. The net posts are outside the doubles court on each side or, for a singles net, outside the singles court on each side. Based on the standard rules of tennis, the size of the court is measured to the outside of the respective baselines and sidelines. The "service" lines ("T" and the "service" line) are centered. The ball must completely miss the line to be considered "out". This also means that the width of the line (except for the center service line) is irrelevant to play. The center service line is , the other lines are between and wide, whereas the baseline may be up to wide. Smaller courts The ITF's Play and Stay campaign promotes playing on smaller courts with slower red, orange, and green balls for younger children. This gives children more time and control so they can serve, rally, and score from the first lesson on courts that are sized to fit their bodies. The ITF has mandated that official competition for children aged 10 years and under should be played on "Orange" courts long by wide. Competition for children under 8 years is played on "Red" courts that are long and wide. The net is always 0.8 m high in the center. Surfaces Tennis is played on a variety of surfaces and each surface has its own characteristics which affect the playing style of