This is an excerpt from Sports Rules Book 4th Edition PDF, The by Human Kinetics & Myles Schrag.
A standard four-walled court is 20 feet wide, 20 feet high, and 40 feet long (see figure 29.1). The recommended minimum height for the back wall is 14 feet. The short line is parallel to the front and back walls; its outside edge is 20 feet from the front wall. The service line is parallel to the short line, and its outside edge is 5 feet in front of the short line.
The service zone is the area between the outer edges of the short line and the service line. The service boxes are located at each side of the service zone. Each service box is marked by a line parallel to the side wall, 18 inches from the wall. The receiver's restraining lines are 5 feet behind the short line. They are parallel to the short line and extend 6 inches from each side wall.