Yup! i call it the rule of 8's--
8 evenly spaced decreases (start at 96 or at 54 or any number in between!--or higher or lower!)
and you get a nice 'half dome' top to a hat.
if you have LOTS OF STITCHES (104. 112, or more!) you are working with a fine yarn (and it take more rows to make an inch!)
if you are working with a few stitches (72, 64 to start) you are working with a bulky yarn and each row is bigger..
but either way, decrease 8 stitches every other round, and you get basically the same shape..
(change the number (of decreases per round) and you change the shape... 9 decrease is still dome like, but 10 decreases EOR get flat (beret like.) 6 or fewer stitch decrease EOR and the hat top gets pointier.. (more like a santa claus hat or witches hat.
Curiously, its not quite the same when you increase.. (especialy if you use YO's as an increase.. )
sometimes 8 increases (YO type) EOR can make a flat (beret like top!
Armed with this information, you can design a hat for any number of stitches, to have any shape crown you want!