One-piece chaise slings are typically 18-24 inches wide and 60-78 inches long, sewn with dowel pockets at the head and foot ends. Installation is the same as a chair sling: pocket over the rail, spline cord into the channel, lock in place.
If your chaise has a fabric break or a horizontal seam between the back and the seat, it is a two-piece chaise — order that variant instead. One-piece slings are more common on poolside chaises and resort-grade lounge chairs.