You need at least 80 sq. m. to build a tennis court, but you will need more if you want to include a practice area and spectators' stands.
Depending on the type of tennis court, you may need as little as 1,000 square feet or as much as 12,000 square feet. Professional tennis courts typically measure 78 by 27 feet (23 by 8 meters), while backyard courts are typically around 60 by 120 feet (18 by 36 meters). For a more detailed answer, please see this article on how to build a tennis court.
