The caps are one-size adjustable. Snapbacks adjust at the back, and the trucker caps use a standard snap closure, so they fit most adults.
The long sleeve tees come in standard unisex sizing. Size options are listed on each product page. If you plan to wear it over another layer, go up one.
What does UPF mean on the tees?
UPF rates how much ultraviolet radiation a fabric blocks from reaching your skin. It is the fabric equivalent of SPF. A UPF shirt keeps working all day without reapplying anything, which matters more on a dock than almost anywhere else, since you are getting sun off the water as well as from above.