That's an excellent and practical question! For a typical urban sidewalk, the most common and recommended size for an outdoor trash can is between 20 to 35 gallons.
This range has become a standard for good reasons. A 20-gallon bin is compact enough to fit on a busy sidewalk without obstructing pedestrian traffic, yet it holds a substantial amount of waste from foot traffic, small snacks, and coffee cups. The 32-35 gallon size is perhaps the most ubiquitous in cities; it offers a great balance of capacity and manageable weight for collection crews when full. Bins this size typically need servicing 1-3 times per week, depending on the foot traffic, which aligns well with municipal collection schedules.
Going much smaller (like 10 gallons) would require emptying multiple times a day in a busy spot, making it inefficient. Going much larger (like 50+ gallons) can lead to bins being overfilled and too heavy to handle easily, creating accessibility issues and potential pest problems if waste sits too long.
The material also matters. In urban settings, you'll often see heavy-duty metal (like galvanized steel) or durable commercial plastic in this size range, designed to withstand public use and weather. Ultimately, the "perfect" size considers specific location factors: a bin outside a busy coffee shop might need a 35-gallon can, while one on a quieter residential block could be perfectly served by 20 gallons. The 20-35 gallon sweet spot provides the flexibility that city planners and business owners need.