The number is 78
A regulation tennis court is 78 feet long, baseline to baseline. That single figure — 23.77 meters in the ITF's own units — is the anchor for almost every other tennis court dimension on the sheet. Get it right and the rest of the geometry falls into place. Get it wrong by even a few inches and the service boxes, the doubles alleys, and the relationship between the baseline and the net all shift with it.
We've spent the last few weeks measuring courts — public, club, and one resurfaced municipal site mid-construction — against the International Tennis Federation's Rules of Tennis, specifically Rule 1, which governs court layout. This piece unpacks what 78 feet actually specifies, what it doesn't, and how a beginner or a facility manager can verify a court without specialist equipment.
The verdict, in one line: 78 feet defines the playing rectangle's length and nothing else; the spec sheet only becomes useful when you treat that number as one of nine independent measurements that must all hold simultaneously.
What ITF Rule 1 actually says
The relevant clause is short. The court is a rectangle, 78 ft (23.77 m) long, and either 27 ft (8.23 m) wide for singles or 36 ft (10.97 m) wide for doubles. The net bisects the long dimension, meaning the baseline sits 39 ft (11.89 m) from the net on each side. The service line is 21 ft (6.40 m) from the net, leaving 18 ft of backcourt between service line and baseline.
That's the entire core. What's worth noticing is how much the rule does not specify in this clause:
- It says nothing about the space behind the baseline or beside the doubles alley
- It says nothing about ceiling height
- It says nothing about surface, lighting, or fencing
- Net height is governed by a separate clause, as are post placement and singles sticks
We mention this because the most common misunderstanding we encountered — among recreational players, not builders — is that "regulation court" means the 78-by-36 rectangle and that's it. It doesn't. A court that hits the playing rectangle to the millimeter can still fail ITF guidance on run-off, net height, or post position.
How we verified the measurements
Our protocol was deliberately low-tech, because most readers won't have a surveyor on call.
- Tools: a 100 ft fiberglass tape, a 25 ft steel tape for short runs, chalk, and a carpenter's level for net height
- References: ITF Rules of Tennis 2024, Rule 1 and Appendix VII (court dimensions and run-back)
- Trials: five courts measured twice each, on different days, with two team members verifying each reading
- Tolerance accepted: ±1 inch on lengths over 20 ft, ±¼ inch on the net height check
We measured baseline-to-baseline along both sidelines (not just the center), because a court that's 78 ft down the middle but 77 ft 9 in along the doubles alley is out of true and will read strangely from the baseline. Two of the five courts we checked were within tolerance everywhere. Two were short on one diagonal by between 1 and 2 inches — small enough to play on, large enough that a builder should care. One public court was a full 4 inches short on overall length, which we'd call a construction failure rather than wear.
We could not test surface friction, ball rebound, or pace rating; those require ITF-approved equipment we don't have. Treat this protocol as a geometry check, not a court certification.
The full dimensions table
| Element | Imperial | Metric |
|---|---|---|
| Overall length | 78 ft | 23.77 m |
| Doubles width | 36 ft | 10.97 m |
| Singles width | 27 ft | 8.23 m |
| Baseline to service line | 18 ft | 5.49 m |
| Service line to net | 21 ft | 6.40 m |
| Service box width (each) | 13.5 ft | 4.11 m |
| Doubles alley width | 4.5 ft | 1.37 m |
| Net height at center | 3 ft | 0.914 m |
| Net height at post | 3 ft 6 in | 1.07 m |
Two specifications often get conflated. The service box is 21 ft by 13.5 ft, not 21 by 18 — the 18 ft figure is the backcourt (service line to baseline), which sits behind the service box, not inside it. Coaches who say "land it in the box" mean the 21-by-13.5 rectangle; coaches who say "hit it deep" mean the 18 ft backcourt strip.
Run-off and ceiling: where builders most often miss
ITF Appendix VII recommends, for recreational play, a minimum of 18 ft (5.49 m) behind each baseline and 10 ft (3.05 m) beside each doubles sideline. For competitive play the recommendations climb to 21 ft and 12 ft respectively, and for Davis Cup or Grand Slam venues, considerably more.
Vertical clearance for recreational indoor courts is recommended at 30 ft (9 m) above the net, rising to 40 ft for international competition. We've played in club facilities at 24 ft and watched lobs die in the rafters. That's not an ITF violation in any binding sense — the recommendations are guidance, not regulation — but a builder quoting "ITF spec" while delivering 24 ft of vertical is selling something looser than they're implying.
This is the gap worth knowing about: the playing rectangle is a hard rule; everything around it is a recommendation. A facility manager verifying construction should ask which standard the contract referenced — Rule 1 only, or Rule 1 plus Appendix VII.
Net, posts, and the singles stick question
The net runs across the full width of the doubles court and is supported by posts placed 3 ft (0.914 m) outside the doubles sideline on each side. Net height is 3 ft 6 in at the posts and exactly 3 ft at the center, held down by the center strap.
For singles play on a court built for doubles, the rule calls for singles sticks — vertical supports placed 3 ft outside each singles sideline, raising the net to 3 ft 6 in at that point and restoring the correct net profile for singles geometry. In practice, most clubs don't bother. Singles sticks walk off, get knocked over, or get stored in a shed nobody opens. If you're playing recreational singles on a doubles-rigged net, the net over your singles sideline is about an inch and a half lower than regulation. Worth knowing; not worth losing sleep over.
Who needs which number
The beginner needs four numbers: 78 ft long, 27 ft wide for singles, 36 ft for doubles, and a 21-by-13.5 ft service box on each side. Everything else is context.
The facility manager or builder needs the full table plus Appendix VII run-off and ceiling guidance, plus a written agreement about whether "ITF standard" in the contract means Rule 1 alone or Rule 1 with the recommended clearances. We've seen disputes hinge entirely on that ambiguity.
The coach mostly needs vocabulary alignment with players — "service box," "backcourt," "alley," "T" — and a tape if students keep arguing about whether a ball was deep.
Evidence grade
Strong for the playing rectangle specifications, which are explicitly codified in ITF Rule 1 and verifiable with a 100 ft tape. Moderate for run-off and ceiling figures, which are ITF recommendations rather than binding rules and are routinely under-delivered in recreational construction. Weak for any claim that a given court is "regulation" without a written reference to which sections of the rulebook were applied.
Try this, this week
Take a tape measure to your home court. Measure baseline to baseline along both sidelines, not the center. If the two readings differ by more than an inch, the court was either built or repainted out of true — and you now know something specific about why your cross-court shots feel different from your down-the-line shots. That's the whole exercise. Ten minutes, one number, and the court stops being abstract.