Tennis court lines explained: what every line means

A tennis court looks busy, but every line has one job: it tells you where to stand, where to serve, and whether a ball is in or out. The names and measurements all come from the ITF Rules of Tennis. Learn the six lines you actually need and the court reads like a map. Here is what each one is called and what it does.

The baseline is the line at the very back of each side, 39 feet from the net. You serve from behind it, and most rallying happens on or near it. A ball that lands beyond the baseline is out. The serve is the one exception to where you stand: you must start behind the baseline and not touch or cross it with either foot until you have struck the ball, or it is a foot fault.

There are two lines down each side a few feet apart. The inner one is the singles sideline; the outer one is the doubles sideline. In a singles match, the court is the narrower 27 feet between the inner lines, and the lane outside is out. In doubles, the court widens to the outer lines and that lane, the doubles alley, is in. Same court, two widths, depending on who is playing.

The service line runs across the court 21 feet from the net, closer to the net than to the baseline, and marks the back of the service area. From it, the center service line runs to the net, dividing the front of each side into two service boxes. Each box is 21 feet deep by 13.5 feet wide (see the full dimensions). A serve must land in the box diagonally opposite the server, past the net but in front of the service line. Land it long, wide, or in the net and it is a fault; miss twice and you lose the point. Once the serve is in, the service boxes no longer matter, the whole court is live.

On each baseline you will see a short tick in the middle, the center mark. It splits the baseline into a deuce (right) half and an ad (left) half so you know which side to serve from: the first point of every game is served from the right, then you alternate. It also marks the inside edge of where you may stand to serve.

Every line counts as part of the court it bounds, so a ball that touches any part of a line, even by a hair, is in. 'On the line is in' is the whole rule. The net itself is not a line but the divider down the middle; for how high it sits, see tennis net height.

Now that the court reads clearly, go use it. Find tennis courts near you and someone to play with. For more on the court, see how big is a tennis court and tennis court surfaces explained. Curious how a pickleball court compares? See pickleball court vs tennis court.