That's an excellent and very practical question! For a standard 50-gallon public waste bin, the best liner bag size is actually 55 to 60 gallons.
Here’s the simple reasoning: a liner labeled for the exact capacity of the bin (50 gallons) will only fit flush with the inner rim. This creates a problem—when you toss in waste, the bag can easily slip down inside. The best practice is to use a liner that's slightly larger. A 55 or 60-gallon bag allows for enough extra material to drape over the top rim of the bin. You can then secure it in place, often with a bungee cord or the bin's own lid.
This "over-the-rim" fit is crucial for public bins. It prevents the bag from falling in, makes removal much cleaner and easier for maintenance staff, and helps contain odors and liquids more effectively. Always look for heavy-duty or contractor-grade bags for public use, as they are more puncture-resistant.
Pro Tip: If you're unsure, quickly measure your bin's height and circumference. A bag's dimensions are usually on the box. You want a bag that's taller than your bin and wide enough to comfortably line it with some excess for folding over. Going one size up is almost always the right move for a neat, secure, and functional setup.