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 78 feet (23.77 metres) long. Its width is 27 feet (8.23 metres) for singles matches and 36 feet (10.97 metres) for doubles matches. The service line is 21 feet (6.40 metres) from the net. Additional clear space around the court is needed in order for players to reach overrun balls for a total of 60 feet (18 metres) wide and 120 feet (37 metres) 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 3 feet 6 inches (1.07 metres) high at the posts, and 3 feet (0.91 metres) high in the center. The net posts are 3 feet (0.91 metres) outside the doubles court on each side or, for a singles net, 3 feet (0.91 metres) outside the singles court on each side.
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 under 10 years of age should be played on "Orange" courts 18 m (59 ft) long by 6.4 m (21 ft) wide. Competition for children under 8 years is played on "Red" courts that are 11 m (36 ft) long and 5.5 m (18 ft) wide. The net is always 0.8 m high in the center.
Tennis is played on a variety of surfaces and each surface has its own characteristics which affect the playing style of the game. There are four main types of courts depending on the materials used for the court surface: clay courts, hard courts, grass courts and carpet courts. The International Tennis Federation (ITF) lists different surfaces and properties and classifies surfaces into one of five pace settings:
Of the current four Grand Slam tournaments, the Australian and US Open use hard courts, French Open is played on clay, and Wimbledon, the only Grand Slam to have always been played on the same surface, is played on grass. The Australian Open switched to hard courts in 1988 and in its early years the French championship alternated between clay and sand/rubble courts. The US Open is the only major to have been played on three surfaces; it was played on grass from its inception until 1974, clay from 1975 until 1977 and hard courts since it moved from the West Side Tennis Club to the National Tennis Center in 1978.