Great question, and the answer is more practical than a single universal number. A standard outdoor bench in a public park is usually a commercial-grade product, not a light residential seat. Most manufacturers rate these benches for a static load capacity of about 500 to 750 pounds total, evenly distributed across the seating surface. Some heavy-duty park benches are rated for 1,000 pounds or more.
In everyday terms, that works out to roughly 250 to 300 pounds per seating position. A typical six-foot bench is designed for two or three adults. If four larger adults sit on it, you might exceed the intended working load, especially after years of weather exposure and use. That does not mean the bench will collapse instantly, but it can bend supports, loosen bolts, crack wooden slats, or wear out fasteners sooner.
What determines the limit? The frame material and design are key. Cast iron, heavy-gauge steel, and thick aluminum frames with reinforced supports tend to carry more weight. Recycled plastic, light tubular aluminum, or thin wooden slats may have lower ratings. Public park benches also often follow commercial furniture standards, so you will see terms like "commercial grade," "static load tested," or a specific capacity listed in the manufacturer's spec sheet.
If you are buying or installing a bench, I would recommend choosing one rated at no less than 750 pounds static load for public use, and making sure it is properly anchored or placed on a stable surface. If you are just curious as a visitor, a standard park bench is safe for two or three average adults, but the rating is for evenly distributed weight, not one heavy point load or a crowd.