That's an excellent and practical question! The short answer is: there isn't one universal, mandatory standard size that fits all municipal trash cans globally or even nationally. However, there are very common *de facto* standards and size ranges that most cities and suppliers adhere to, making it easier for public works departments and residents.
The most typical size you'll encounter for standard rectangular or round public litter bins is the 33-gallon bag (often labeled as 30-33 gallons). This bag usually measures around 24 inches wide by 33 inches tall (approx. 61 cm x 84 cm) when flat and open. It's designed to fit classic "town square" style cans perfectly. You'll also frequently see 45-gallon bags for larger containers, often measuring about 34 inches by 40 inches (86 cm x 102 cm).
The size needed depends heavily on the specific trash can model used by a municipality. Factors like can shape (round vs. rectangular), depth, and opening diameter all matter. Furthermore, cities often procure bags through bulk contracts with specific manufacturers, effectively creating a local "standard" for their fleet.
For household collection, where residents use city-provided rolling carts, the bag size is essentially the cart's capacity itself (e.g., 64-gallon cart), though many people use standard 13-gallon kitchen bags inside their homes.
So, while not officially standardized like an electrical plug, common practice and industrial supply have settled on a few popular sizes. If you need bags for a public can, the best approach is to measure your bin's interior or check with your local public works department for their recommended specification.