That's a great question, and one that really matters for keeping a playground clean and safe. There isn't a single magic number, as the right size depends on a few key factors. A good starting point is a 20 to 32-gallon can. This size is common, manageable for maintenance staff to empty, and often sufficient for smaller neighborhood parks.
For larger, high-traffic playgrounds, you might need multiple cans or step up to a 44 or even 64-gallon capacity. The main things to consider are how busy the playground gets, how often it's serviced, and where you place the bins. A can near a picnic area will fill faster than one by the swings. The goal is to choose a size that prevents overflow between collections, which can attract pests and create litter. Ultimately, observing your specific site for a week or two is the best way to gauge the perfect capacity for your needs.