I measured my head because I know I have a smaller than generally average head, my measurement fit into the petite range, so I ordered that. I also ordered the Terra/Aviator fit for my sunglasses because that was what was suggested based on the style of sunglasses I wear. When I wore the hat, while it did fit, I felt like too much of the Velcro was exposed so my hair kept getting caught in it, then it felt itchy/rough on my forehead (So I tried washing it to soften it--didn't really help so I powered through it as I have definitely dealt with worse things in my life), the bill of the hat still pressed down on my sunglasses (no matter which pair I was wearing; I eventually tried to unbend it, which sorry if helped with ONE PAIR of my sunnies)... And when I took off my sunglasses, for mostly obvious reasons, seeing the notches in my peripherals drove me (more so my ADHD and OCD) absolutely up the wall for at least the first 10 minutes-- I would eventually adjust to this and just like not seeing your nose, I would go blind to them... I do think I'm going to order another one. I'm just not sure if I want to order the same notch measurement, and I'm certainly not going to order the same size....