That's an excellent and practical question! As someone who specifies and installs park furniture, I can tell you there's no single universal number, but typical commercial-grade metal park benches are engineered to hold a significant amount. The short answer is that a well-constructed, permanently installed metal bench designed for public use can generally support 800 to 1,000 pounds (360 to 450 kg) distributed evenly across its seat.
However, this isn't just about the metal itself. The true capacity depends on several key factors. First is the bench classification. Residential or light-commercial benches might hold 400-600 lbs, while heavy-duty commercial or municipal benches are built to the 800-1000+ lb standard to withstand constant public use. The installation method is critical: a bench anchored with concrete footings into the ground is far more robust than one simply placed on a surface. The design and material matter too; cast iron or heavy-gauge steel frames with reinforced legs and cross-bracing are much stronger than thin, tubular designs.
Manufacturers often provide a static load rating (evenly distributed weight) and a more important safety factor (usually 3:1 or 4:1). This means a bench rated for 1,000 lbs is designed not to fail until 3,000-4,000 lbs, accounting for dynamic forces like people plopping down or shifting. For public parks, always look for benches meeting BS EN 581 or ASTM standards for outdoor furniture, which test for stability and strength. Remember, regular maintenance to check for rust, weld cracks, or loose anchors is essential to ensure any bench maintains its rated capacity over years of weather and use.