This pattern is knit in the round in two sections. It can be made as a hat or as a crown without the hat.
If you are making the hat, please note the section in the pattern that discusses the eyelets, they add a good deal of stretch, so you might want to consider sizing down if you want a snug fit. As discussed in the pattern, the measurements given are finished measurements taken flat, without stretching. If you are making the crown without the hat, there is not as much stretch in the pattern. Measure the head at its widest point and choose the comparable finished measurement to get the size desired.
Photos by Matt Bowen for Wiley Press.