You could knit a swatch of the worsted, figure out what your stitches per inch would be, then going by the measurements on the schematic, figure out which size would be appropriate for your gauge. Does that make sense?? You would wind up making a smaller size than you would normally be (unless you're already a XS, then you might be out of luck!! ) because you would be getting less stitches per inch.
Or you could follow these directions:
Very cool, and I think that this would be a basic enough item for the calculations to not be too crazy.
(Can you tell I want you to join me????? :lol: )