How can I tell what size canopy I have?

To determine the width, measure from outside the frame to outside the frame.  Floe offers canopies that are 8, 9, 10, 10.5, and 11.5' wide.  To determine the length, count the spaces between the hoops which are 2'.  If you have 10 spaces it is a 20' canopy.  Your old canopy should also have a tag sewn into an inside corner with year of manufacture and size.