The service line is one of the most useful markings to understand on a tennis court. It sets the back edge of each service box, helps players judge whether a serve is in, and gives returners a clear reference point for positioning. If you are learning the game or checking a court near you, knowing where this line sits makes the layout much easier to read.
On a standard court, the service line is 21 feet from the net and runs between the singles sidelines. That distance shapes the service boxes on both sides of the net. It also explains why a serve can land beyond the service line and still be a fault, even if it looks close to the baseline.
Where Is the Service Line on a Tennis Court?
Look toward either end of the court from the net. The service line is the horizontal line across the court that forms the far edge of the service boxes. It is parallel to the net and sits halfway between the net and the baseline.
The line does not extend across the doubles alleys. It runs from one singles sideline to the other, making it 27 feet long. A center service line runs from the net to each service line and splits the space into two service boxes: the deuce court on the player’s right and the ad court on the player’s left.
| Court marking or area | Standard measurement | What it tells you |
|---|---|---|
| Court length | 78 feet | Distance from baseline to baseline |
| Net to service line | 21 feet | Depth of each service box |
| Service line length | 27 feet | Width between the singles sidelines |
| Each service box | 13.5 feet wide by 21 feet deep | Target area for a legal serve |
These measurements are the same on singles and doubles courts. A doubles court has extra width outside the singles sidelines, called the alleys, but those alleys are not part of the service boxes.
What Does the Service Line Do?
When serving, a player must hit the ball into the diagonally opposite service box. The target box is bounded by the net, the center service line, the singles sideline, and the service line. The ball must bounce inside that area or touch one of its boundary lines.
That last detail matters: a serve that lands on the service line is in. The same is true if it catches the center service line or the relevant singles sideline. Court lines count as part of the area they mark. A serve that lands beyond the service line, however, is long and counts as a fault.
In doubles, the service boxes are still limited by the singles sidelines. A serve that lands in the doubles alley is out, even though the alley is used during the rest of a doubles rally. Once the serve is returned, the full doubles court—including both alleys—is in play.
How the Service Line Affects Play
It helps you judge serve placement
Servers often use the service line as a visual depth reference. A serve aimed near the line can push a receiver back or make them reach, while a shorter serve can pull them forward. The trade-off is risk: aiming close to the back of the box leaves less room for error.
For example, a player serving from the deuce court might target the receiver’s backhand with a slice serve that curves toward the singles sideline. The serve still has to land inside the service line. If it lands just beyond that line, the placement does not matter—it is a fault.
It gives returners a positioning cue
The service line can help a receiver estimate how much time a serve will give them. A player standing near the baseline may have more time to react to a slower serve, while stepping inside the baseline can put them in a better position to attack a weaker delivery. The right spot depends on the server’s pace, spin, and accuracy, as well as the court surface.
There is no single correct distance from the baseline. Against a powerful first serve, a player may stand farther back to gain reaction time. Against a slower second serve, they might move forward and look to take the ball early. The service line is not where a returner must stand; it is simply a useful landmark when reading the court.
It helps with serve practice
During practice, use the service line to set clear targets. Rather than trying to hit every serve as close to the back of the box as possible, aim for a safe area first, then vary direction and depth. A cone or marker placed well inside the line can give a beginner a more forgiving target than the boundary itself.
How to Check or Measure the Service Line
If you are inspecting a court, start at the net and measure 21 feet toward each baseline. The service line should sit across the court at that point, from singles sideline to singles sideline. The center service line should meet it at a right angle and continue toward the net.
For a quick visual check, compare the service line with the baseline: it should be halfway between the net and baseline. If a court has faded or uneven markings, confirm which lines belong to singles and doubles play before starting. The inner side lines mark the singles court; the outer lines mark the doubles court.
Line width can vary within tennis regulations, and painted lines may look wider or narrower depending on the surface. What matters during play is whether the ball touches the marked line. On clay, players may also inspect a mark after a close call, while on hard courts the line itself is usually the clearest evidence.
Frequently Asked Questions
Is the service line part of the service box?
Yes. The service line forms the back boundary of the service box, so a serve touching it is in. A serve that lands completely beyond it is long.
How far is the service line from the net?
On a standard tennis court, the service line is 21 feet from the net. The service box is 21 feet deep, measured from the net to the service line.
Does the service line go across the doubles alley?
No. It runs between the singles sidelines, so it is 27 feet long. The doubles alleys are outside the service boxes and are not valid serve targets.
Can a player stand inside the service line to return a serve?
Yes. A receiver can stand anywhere on their side of the court, including inside the service line, as long as they do not interfere with the serve. Players choose their position based on the server and the time they need to react.
Final Thoughts
The tennis court service line marks the back of each service box, 21 feet from the net. It is a simple line with an important job: it helps define a legal serve, gives players a target for placement, and offers a useful reference for practice and court checks. Once you can spot it quickly, the service boxes—and the serve rules built around them—are much easier to understand.
