From the designer’s note:

Gauge is not critical, but I got 14 stitches and 20 rows per 4 inches in Garter Stitch Eyelet pattern.

Finished mobius is 6 inches wide and about 40 inches around. To fit most people.

Originally published on About.com, currently found on The Spruce. (I am no longer affiliated with the company so I cannot edit pages there. They redirect and delete pages a lot so you may want to download/print to save.)

It should be noted that the photo on the website has nothing to do with the instructions. The photos here are accurate.