Garter stitch pinwheels are fun to knit. Short rows provide the shaping, and the squareness of the garter stitch/ridge makes the math easy. The plastic wrapper is what turns this pinwheel into Christmas candy.
Yes, with pinwheels, we’re back to pi times diameter. But you don’t have to know about that, because you can knit a pinwheel without a pattern. All you have to know is how far across you want the circle to be, and how many “slices” you want to divide it into (multiples of six are best).
I explained it all in “Round and Round with Garter Stitch,” INKnitters, pp. 78 ff., Vol. 3, No. 11, Winter 2003. Bonus information in this issue: turning pinwheels into ovals and hearts. And a Valentine heart pattern, knitted with Brown Sheep’s Cotton Fleece. In the issue before that, I wrote about garter squares, and how to knit quilt-ish motifs without a pattern. You may be able to find issues of INKnitters online at eBay or etsy.