Size of foot will determine gauge and needle size.
Description from Knitty.com
When choosing a variegated yarn for this project, look for one with short stretches of each color (6-8 inches) to avoid pooling or flashing. I think the variegation and lace complement each other nicely in this instance, but have included an example in a solid sock yarn as well.
To fit foot circumference: 8 (9, 10) inches;
Foot circumference = 7.25”(8”, 9”);
Sole length is adjustable to fit the individual’s foot;
Cuff length = 6” or as desired;
Gauge: 40 (36, 32) stitches = 4 inches in pattern stitch.