Most tennis courts are designed and constructed to accommodate doubles matches, wherein two players play against two opponents at the same time. Singles matches are played on the same court, using a different set of game lines, demarcating a narrower out-of-bounds. The tennis court size for a doubles match is 54 inches wider on each side of the center line than a singles tennis court.
According to the international tennis rules, each tennis net support post or stile shall be positioned 36 inches outside the out-of-bounds line, lifting the tennis net at that point to a height of 42 inches. As the tennis net sags towards the center, it shall measure 36 inches above the court center line. Since virtually all tennis courts are built to accommodate doubles matches, it is common practice for the distance between the tennis net support posts or stiles to be fixed at the larger distance for doubles matches, rather than the shorter distance for singles practice.