In tennis, the service line helps define the area in which a serve must land before it can be returned. It is the outermost boundary where a serve must land before it is returned. On a standard regulation court, the service line is drawn parallel to the net, at a distance of 21 from the net. The service line is 27 feet wide, ending at the singles sideline.
The service line is the outermost boundary of the service box. If a serve lands beyond the service line, it is a fault. However, a serve may land on the service line itself and still be considered a good serve.
The center service line divides the service area of the court into two equal boxes, called the service boxes.The center service line establishes the rest of the service box, with the help of the singles' sidelines.
The center line runs perpendicular to the net, dividing the area between net and service line into two equal boxes that are 21 ft. x 13.5 ft. in area. These two boxes on either side of the court are called the left and right service boxes.
The tennis service box is a rectangular area to which the player serving must aim their serve. For a serve to be considered a "good serve," the ball must bounce in the service box before being returned by the other player. If a serve lands outside the designated box, it is an invalid serve, or "fault," and must be re-served.
When serving, a player stands behind the baseline of the court (backmost boundary of the court), and must send the ball into the service box diagonally across from where they are serving. Although the total court size in singles games is smaller than in doubles games, the service box is the same for both.