Measuring st stitch

I just started my second hat project, a hemmed hat. It says to do a stockinette stitch until it is 7 1/2 inches. I was wondering do I unroll the bottom to include that in my measurement or do I keep it rolled?

Also, the pattern I am using is from Knitting Pure and Simple. Unlike my first hat, it doesn’t have different measurements for different sizes. Is this common in a hemmed hat and I’m not really understanding the concept of this hat? It was recommended to me by the people at the yarn store where I live for a hat for my grandfather so I went with it, but I’m starting to get a little concerned that I’m going to finish it and it won’t fit him.

Thanks so much in advance!

It should be measured flat, so flatten out the edge, but don’t stretch it. If it’s an adult pattern, they’re pretty much all the same size, so there would be only one measurement.