A tennis court is fixed by its markings.

How to read the court before a point

1. Identify whether the point is singles or doubles, because that decides which sidelines are the rally boundaries.
2. Use the baselines at the ends of the court and the relevant sidelines at the sides to define the live rally court.
3. For a serve, ignore the baseline target and look only at the correct diagonal service box.
4. Remember that a ball touching any part of a relevant line is in.
5. If singles is played on a doubles net, check whether singles sticks are being used and treat the outer net posts and net outside the singles sticks as permanent fixtures.

This page covers the full-size tennis court

These dimensions describe the standard full-size court used under the Rules of Tennis. Separate 10-and-under red and orange court formats, beach tennis, padel, pickleball, short-court coaching drills, and local recreational layouts can use different sizes. A competition can also set stricter facility standards around the court without changing the court's basic markings.

The court is 78 feet long

The court is a rectangle 78 feet (23.77 m) long from baseline to baseline. The net crosses the court at the middle, so each half of the court is 39 feet long.

The width depends on the format. For singles, the court is 27 feet (8.23 m) wide. For doubles, it is 36 feet (10.97 m) wide. The extra space is split into the two doubles alleys, each 4 feet 6 inches (1.37 m) wide.

The visible court is not always the playable court

Most courts are marked for both singles and doubles. In singles, the inner sidelines are the rally boundaries and the doubles alleys are out. In doubles, the outer sidelines are the rally boundaries after a legal serve is in play.

The service box does not get wider in doubles. A serve must still land in the correct diagonal service court bounded by the singles sideline, centre service line, service line, and net.

The service line sits 21 feet from the net

On each side of the net, the service line is drawn between the singles sidelines 21 feet (6.40 m) from the net and parallel to it. The area between the service line and the net is divided in half by the centre service line, creating the right and left service courts.

This is why a deep serve near the baseline is a fault even if it lands inside the singles court. The serve's legal target is the diagonal service box, not the full rally court.

The baselines close the court at each end

The baselines are the lines at the ends of the court. Each baseline is divided by a centre mark, 4 inches (10 cm) long, drawn inside the court and parallel with the singles sidelines.

The centre mark matters most for service position. Before striking the serve, the server must stand behind the baseline and within the imaginary extensions of the centre mark and the relevant sideline for that point.

The line belongs to the area it marks

A tennis line is not out-of-bounds by itself. If the ball touches the line, it is treated as touching the court bounded by that line. That applies to baselines, sidelines, service lines, and the centre service line.

For practical line calls, this means a ball clipping the outside edge of a relevant line is still good. A ball that lands completely beyond the relevant line is out.

Measurements are made to the outside of the lines

All court measurements are made to the outside of the lines. The centre service line and centre mark are 2 inches (5 cm) wide. Other court lines are between 1 inch (2.5 cm) and 2 inches (5 cm) wide, except that baselines may be up to 4 inches (10 cm) wide.

All court lines must be the same colour and clearly contrast with the playing surface. The measurement rule keeps the legal court size from changing just because a permitted line is painted wider or narrower.

The net is higher at the posts than at the centre

The net is suspended across the middle of the court. It is 3 feet 6 inches (1.07 m) high at the posts and 3 feet (0.914 m) high at the centre, where it is held down by a white strap.

For doubles, the centres of the net posts are 3 feet (0.914 m) outside the doubles court on each side. For singles with a singles net, the posts are 3 feet outside the singles court. When singles is played on a doubles net, singles sticks support the net 3 feet outside the singles court on each side.

Singles sticks change what counts as the net

In singles played with a doubles net and singles sticks, the singles sticks define the useful net area for the singles court. The net posts and the part of the net outside the singles sticks are permanent fixtures, not part of the playable net for that singles point.

This matters when a ball hits something around the court. Under the permanent-fixture rule, a ball that hits a permanent fixture before landing in the correct court loses the point for the player who struck it. If it hits a permanent fixture after already landing in the correct court, the player who struck it wins the point.

Clearance around the court is separate from the court

The playable court ends at the lines, but safe play also needs space behind the baselines and outside the sidelines. The ITF gives recommended minimum run-off distances for international competition, recreational play, and club play, but those are facility guidance rather than a change to the 78-by-27 or 78-by-36 court dimensions.

Events, clubs, and venue operators can require more space for safety, television, officials, ball persons, or temporary structures.

Misunderstandings to avoid

• "The doubles alley is always in" is wrong. It is in for doubles rallies, but out for singles rallies.
• "The service box widens for doubles" is wrong. The serve must still land inside the standard diagonal service court.
• "A ball on the line is out" is wrong. The line belongs to the area it marks.
• "The net is the same height everywhere" is wrong. The centre is lower than the posts.
• "Run-off space is part of the court" is wrong. Players may move there to play a ball, but it is not part of the court's measured rectangle.

How court markings are enforced

Officials use the markings to decide the first relevant question: whether the match is singles or doubles, whether the serve landed in the correct service box, whether a rally ball touched the correct court, and whether a fixture contact happened before or after a legal bounce.

If a court marking is unclear, unsafe, or incorrectly prepared, the referee or event authority handles it under the competition's procedure. During play, the underlying interpretation stays the same: choose the relevant line, remember that the line belongs to the area, and judge the ball against that boundary.

Source material

• ITF Rules and Regulations
• ITF Rules of Tennis
• USTA Friend at Court