Tennis court dimensions and what each line means

Read the lines. Read the angles.

Key facts

1
A tennis court is 23.77 m long, 8.23 m wide for singles and 10.97 m wide for doubles, with each doubles alley about 1.37 m wide.
ITF Rules of Tennis
2
The net is 1.07 m high at the posts and 0.914 m at the centre strap, a sag of 0.156 m by design.
ITF Rules of Tennis
3
Each service box is about 6.40 m deep and 4.11 m wide.
ITF Rules of Tennis
4
A ball hit corner to corner in singles travels about 25.15 m, against 23.77 m straight down the line.
Computed from ITF singles dimensions, 23.77 × 8.23 m
5
In doubles the alleys count only after the serve, and the service boxes don't change.

Why it works

Every line on a tennis court encodes a rule. The centre service line decides which box the serve must find, and the serve must land in the diagonal box. The baseline and the centre mark define where the server stands, and crossing either before contact is a foot fault.

The geometry is the tactic. A cross-court ball travels the diagonal, about 25.15 m, and crosses the net near the middle where it's lowest. A down-the-line ball has only 23.77 m and crosses near the post where the net is highest.

That's why coaches say rally cross-court and change direction only with a clear opening, the 70/30 rule of thumb. The court's shape decides the percentages before you decide anything.

The line to say on court
“Longer court, lower net. That's why cross-court.”

Drill: Name the line

30 min · alone

Watch a match. Every time a ball lands near a line, name the line and the rule it enforces before the replay.
On every serve, say which box it must find and whether the server's feet were legal.
On every rally ball, say "cross" or "line" and which net height it had to clear.

Number to beat15 lines in a row named with their rule before the replay

Faults and fixes

Thinking singles and doubles use the same court

The width differs by 2.74 m, and the alleys come into play after the serve.

FixPicture the alleys switching on once the serve lands.

Thinking the net is one flat height

It sags 0.156 m to the middle by design.

FixMeasure your own net at the posts and the centre strap.

Treating lines as just boundaries

Each line enforces a specific rule.

FixLearn the rule for each line, not only where it is.

Thinking the alleys count on the serve

The service boxes don't change in doubles.

FixServe to the box. The alleys are for the rally.

Questions players ask

How high is a tennis net?

0.914 m at the centre strap and 1.07 m at the posts. The net sags 0.156 m to the middle by design.

How big is a tennis court?

23.77 m long, 8.23 m wide for singles and 10.97 m wide for doubles. Each service box is about 6.40 m deep and 4.11 m wide.

Do the doubles alleys count on the serve?

No. The service boxes are the same in singles and doubles. The alleys count only after the serve.

Why is cross-court the safer shot?

The diagonal gives you about 25.15 m of court instead of 23.77 m, and the ball crosses the net near its lowest point in the middle.

What this doesn't cover

The dimensions come from the ITF rules. The 70/30 cross-court heuristic is a coaching rule of thumb, not a measured constant, and a clear opening can still make the line the right shot.

Sources

ITF Rules of Tennis: court dimensions and net heights

Play the pointWhen to hit cross-court or down the line in tennisHit cross-court as your default and go down the line only when the court opens: the ball is short, you're inside the baseline and your opponent is wide. Cross-court crosses the net where it's lower, travels into a longer court, and brings the reply back to your side. Down the line reverses all three.Know the gameTennis rules explained: let, fault, foot fault and hindranceYes. A serve that clips the net cord and still lands in the correct box is a let, and the serve is replayed with no penalty. If it clips the net and lands out, it's a fault. Without an umpire, The Code applies: call only your own side, give your opponent the benefit of the doubt, and announce the score before each serve.Move and reactWhere to recover after your shot in tennisAfter you hit, recover to the line that splits your opponent's widest possible replies, not to the centre mark. That bisector moves with where they hit from: it matches the centre mark only when they are in the middle. After a sharp cross-court, it sits toward the side you hit from, so you can reach both of their widest replies.Play the pointWhere to stand in doubles: standard, I and AustralianIn doubles, pick the serving formation that takes away the returner's favourite shot. The default is standard: the server about halfway between the centre mark and the doubles sideline, the partner at the net guarding the alley. If the cross-court return is hurting you, go Australian to remove it. The I-formation makes the returner guess which way you'll move.