The doubles line is the outer sideline that makes a tennis court wider for doubles than for singles. Knowing when that line counts—and when the narrower singles sideline still applies—clears up common arguments over serves, rallies, and balls near the edge.
On a standard court, the doubles sidelines are 36 feet apart, while the singles sidelines are 27 feet apart. The strip between each pair is called the doubles alley. It is part of the court during doubles rallies, but it is not a valid target for a serve.
Which Line Is the Doubles Line?
Each side of a tennis court has two long sidelines. The inner sideline marks the singles court; the outer sideline marks the doubles court. The space between them is the doubles alley, also called the tramlines.
The lines run parallel to each other from the baseline toward the net. Each doubles alley is 4.5 feet (about 1.37 metres) wide. Together, the two alleys add 9 feet to the court’s width for doubles play.
| Court marking | What it marks | Width across court |
|---|---|---|
| Singles sidelines | Side boundaries for singles | 27 feet |
| Doubles sidelines | Side boundaries for doubles | 36 feet |
| Doubles alley | Strip between a singles and doubles sideline | 4.5 feet per side |
| Court length | Baseline to baseline | 78 feet |
The court’s length stays the same in singles and doubles. It is the sidelines that change which playing area is in use.
When Is the Doubles Line In?
During a doubles rally, the outer doubles sidelines are the side boundaries. A ball that lands in the alley is in, even if it would have been out in singles. The alley gives doubles teams extra width for cross-court shots, passing shots, and defensive lobs.
For example, if a groundstroke lands between the singles sideline and the doubles sideline, it is a good shot in doubles. If it lands beyond the outer doubles line, it is out. The same rule applies at the baseline: a ball touching the baseline is in, while one landing completely beyond it is out.
A line belongs to the court it marks. So if any part of the ball touches the doubles sideline during a doubles rally, the ball is in. The call is based on the ball’s contact with the court, not where it looks to be from a player’s position.
Why the Doubles Line Does Not Count on Serves
A serve has a narrower target than a doubles rally. The serve must land in the correct diagonal service box, which is bounded by the center service line and the singles sideline—not the doubles sideline. A serve that lands in the alley is a fault, even in a doubles match.
This can catch new doubles players out. A serve may look as though it has landed inside the overall doubles court, but if it is outside the singles sideline, it has missed the service box. Once the serve lands in the correct box and the return is played, the full doubles width becomes available for the rally.
A practical way to remember the rule is: narrow for the serve, wide for the rally. The server aims for the same-width service boxes used in singles; both teams use the doubles sidelines once play moves into the point.
How the Doubles Line Changes Tactics
The extra width creates both opportunities and risks. A cross-court shot can travel farther into the alley and still stay in, giving a doubles player more room to pull an opponent away from the middle. The same space also gives the net player a tempting target for a sharp angle volley.
That does not mean every ball should be aimed at the outside line. Aiming too close to the doubles sideline leaves little margin for error. On a windy day or under pressure, a shot a foot inside the line is often the smarter choice. The extra court width helps most when players use it to open space, not when they try to paint the line on every shot.
For a simple example, imagine the receiving team’s returner is pulled wide. A controlled cross-court shot into the opposite alley can force the other team to cover more ground. But if the shot drifts beyond the outer sideline, the point is over. In doubles, good court awareness means knowing the wider boundary while still choosing a target with enough margin.
Common Doubles-Line Mistakes
- Calling a ball in the alley out: The alley is part of the playing area during doubles rallies.
- Accepting an alley serve: A serve landing outside the singles sideline is a fault, even in doubles.
- Confusing the two sidelines: The inner line is for singles; the outer line is for doubles.
- Calling a ball out because it touches the line: A ball that touches the relevant boundary line is in.
- Judging from the wrong position: Players should make calls from a clear view of where the ball lands, rather than guessing from across the court.
On courts with faded or crowded markings, it can help to identify the outer doubles sidelines before warm-up. If players disagree during a casual match, pause and agree on which line is being used. In organized play, follow the event’s rules and the officials’ calls.
Frequently Asked Questions
Is the doubles alley in or out?
It is in during a doubles rally. The ball must land inside or touch the outer doubles sideline to count as good.
Can a doubles serve land in the alley?
No. A serve must land in the correct diagonal service box, which ends at the singles sideline. Landing in the alley is a fault.
How wide is the doubles court?
The doubles court is 36 feet wide, compared with 27 feet for singles. Each doubles alley adds 4.5 feet along one side.
Is a ball on the doubles line in?
Yes. If any part of the ball touches the doubles sideline during a rally, it is in. On a serve, the singles sideline defines the side of the service box instead.
Final Thoughts
The doubles line is the outer sideline, and it brings the alleys into play during rallies. Serves are the key exception: they must land inside the narrower service box, beyond the singles sideline’s boundary. Keep the simple rule in mind—narrow for the serve, wide for the rally—and the court markings become much easier to read.
