That's an excellent question that gets to the heart of practical urban design. There's no one-size-fits-all number, but a solid starting point is 3-5 well-placed bins for a typical one-block plaza. The key word is "well-placed." Let me break down the logic.
First, consider pedestrian flow and "touchpoints." Place bins at natural gathering spots: near seating areas, at plaza entrances/exits, close to food vendors or kiosks, and beside transit stops. A bin should be within a 30-second walk from any point. People won't hunt for a trash can.
Next, think capacity and collection. For a busy plaza, two large-capacity (50-60 gallon) bins at primary nodes and 2-3 smaller ones at secondary spots often work. This prevents overflow, which is a major eyesore and hygiene issue. Your maintenance schedule is crucial—more bins mean more collection points but can streamline labor if planned well.
Finally, observe and adapt. Install a baseline number, then watch for "trash trails" (litter leading to a full bin) or consistently empty containers. Be ready to adjust. The goal is seamless integration: enough bins to keep the space clean without cluttering the design.
In short, start with 3-5 bins strategically located at high-activity zones, ensure they are adequately sized and regularly serviced, and use real-world observation to fine-tune. A clean plaza is a used and enjoyed plaza.