That's a great practical question! The capacity of a standard-sized urban trash can you see on sidewalks and in public parks can vary, but there are common ranges. The classic cylindrical or rectangular public litter bins typically hold between 20 to 50 gallons (about 75 to 190 liters). You can think of the smaller ones as roughly the size of a large kitchen trash can, while the larger ones might be as big as a standard drum.
For larger, commercial-style containers near restaurants or in apartment complexes, capacities jump significantly. These often range from 60 gallons up to 300 gallons or more. The specific size a city chooses depends heavily on location foot traffic and collection frequency. A busy downtown square will need larger or more frequently emptied bins than a quiet residential street.
It's interesting to note that many cities are standardizing sizes to streamline collection using automated truck arms. So, while the classic green wire-mesh basket might hold around 25 gallons, you're increasingly seeing sturdy, plastic 35- or 50-gallon bins as the new "standard" for municipal waste collection in public spaces.