That's a great and practical question! It's something many of us don't think about until we're trying to cram that last bulky item into an already full bin. For a standard municipal or commercial urban trash bin—the typical wheeled carts provided by waste services—the lid itself isn't designed to hold significant weight. There's no official, universal weight rating like you'd find on furniture.
In practice, these plastic lids are meant to close securely and keep pests and weather out, not to function as a shelf. Most are made from durable polyethylene, but their strength comes from the hinge and support structure when closed. Placing constant or heavy weight on an open lid can easily crack it or damage the hinge pins. A general rule of thumb from waste management professionals is that you should avoid placing more than 10-15 pounds (4.5-7 kg) of direct, sustained pressure on an open lid. This could be the weight of an overfilled bag resting on it or someone leaning on it.
The real capacity concern is for the entire bin. Standard 64-gallon wheeled carts often have a maximum load capacity of 200-250 pounds. Exceeding this, or improperly distributing weight, can break the wheels or body. So, while the lid is a weak point, the best practice is to never overload the bin itself, ensure the lid can close fully, and never use the open lid as a support for heavy items. If you regularly have heavy waste, contacting your local waste authority for guidelines or special collection services is the safest approach.