This informative chart comes from "Flat Flip Flies Straight!: True Origins of the Frisbee" book. It beautifully compares the diameter and cross-section from the original Flyin-Saucer (1948) design to a Flying Saucer (1957) to a Regular Frisbee - and some other popular disc brands.
Fascinating to see the differences between these early plastic flying discs. Look at the progression of these disc's rims; the slope started severe like a house roof (Flyin-Saucer) and gradually became more aerodynamic. As a comparison, today's disc for the sport of ultimate = 10.75" wide.
[chart via Flat Flip Flies Straight!]