Great quality panama hat. The tag on the inside says large. My head fits a 7 1/4 - 7 1/2 and this hat fit nicely. It has a nice padded inner band which may have aided in the fitment and comfort. inside measurements are 22.5-22.75 circumference 8" front to back, and 7" side to side.
May or may not have come from the Optimo Hats company, where they still today make hats by hand. No obvious tags or markings for manufacture other than it was made in USA.
The Optimo shape was a staple profile in the first half of the 20th century, but it still retains its appeal and elegance today. With a distinctly British expat feel, this style is defined by a top seam along the center of the rounded crown.