[Den]

It depends on the pattern. Some patterns will give you how many stitches to cast on/increase/decrease for each size, including in key points of the pattern itself. Those ones are already calculated, but some patterns, like the hat I'm going to make for a dear friend, I have to do math.

Thankfully, the pattern I'm using, I already calculated how many more stitches I have to cast on, and I know where I can add stitches without it fucking up the design.