What size beam is required for a 16 foot pergola?

The size of the beam required for a 16-foot pergola depends on several factors, including the type of wood used, the spacing of the posts, and the load it needs to support (such as snow or wind loads). Generally, a 2x8 or 2x10 beam made of pressure-treated lumber or a similar material is commonly used for spans of this length. It's important to consult local building codes and possibly an engineer to ensure safety and compliance.