That's a great question, and one that many people don't think about until they're standing there with a new roll of bags. The short answer is: it's complicated. Most public or urban trash cans are not designed for a single, universal liner size. The reality is that you will likely need a specific size for your particular bin.
Think of it like buying shoes; one size does not fit all. The dimensions of public trash receptacles can vary significantly depending on the manufacturer, the location (like a park versus a city sidewalk), and their intended capacity. Using a bag that is too small can lead to messy tears and spills, while one that is too large is wasteful and may not secure properly under the rim.
So, how do you find the right size? The most reliable method is to measure your specific trash can. You'll want to measure the circumference of the top opening and the depth (or height) of the can itself. With these measurements, you can check the product specifications on any box of liners to find a compatible match. Many liner manufacturers provide sizing charts for this exact purpose.
For standard round bins, common sizes are often referred to by their gallon capacity, such as 30-gallon or 55-gallon bags. However, for uniquely shaped or rectangular urban cans, you might need to look for specialty liners. Your best bet for public bins is to check with your local municipal waste management department, as they often have information on the specific models used in your area and may even provide the correct liners to residents. In short, while a "universal" fit isn't standard, finding the right specific size is straightforward with a little bit of measuring.