Gauge is based on the yarn and needles you use - you should be knitting a tight fabric, with needles one or two sizes below recommended for your yarn. The general idea is to get the width of the headband to be equal to or greater than the length of your ears, thus fully covering them. Good luck.

Based on the beginning of Coronet, by Alexandra Virgiel, featured in the Winter 2003 edition of Knitty.