Now that you've started knitting your stripes, it's time to think about how long the Body of your Hat should be.
The two Crown shapings I've written for this tutorial come recipe come pattern are short in their length - one is a gathered crown, the other a square (or wonky?) top - and this means that we can work the Body of the Hat to almost the desired overall length.
To measure the length on a wonky Hat with short row stripes, you'll want to take the average length - measure at the longest part and measure at the shortest part, add them together then divide it by two. You'd then treat this average length as you would any length when measuring the Body.
The overall length of your Hat, including the Brim, would be somewhere in this range:
14in: 5in - 5.5in/12.75cm - 14cm
16in: 5.5in - 6in/14cm - 15.25cm
18in: 6in - 6.5in/15.25cm - 16.5cm
20in: 6.5in - 7in/16.5cm - 17.75cm
22in: 7in - 7.5in/17.75cm - 19cm
24in: 7.5in - 8in/19cm - 20.25
I generally allow 1in/2.5cm difference between sizes when I write patterns for slouchy Hats, but it's important to remember that this is variable, and that it depends on how much slouch you want, how much extra width you added and more, and this is where it's uber helpful to know how well other (esp. Woolly Wormhead!) Hat patterns fit. If you know that you have a long face and quite a deep ear to Crown measurement, you'll want to make your Hat on the longer side. Conversely, if you've learnt that your ear to Crown measurement is shallower than average, don't knit it quite as long.
If you're still unsure, try thinking about it a different way: measure the depth of your head, from the base of your ear to your Crown (more info is on the Sizing page). Know that the Crown shaping of your #wwscrapalong Hat itself is short (a few rows, essentially - it's unlikely to be any more than 1in/2.5cm for the gathered version). This means that you can work the length of your Hat until it is the same length as your head, and allow the crown shaping to be that extra bit of depth needed for slouch.
Another way to approach it might be this: knit it to a length you like the look of. Place the Hat on your head, gather up the stitches on your circular needle (without taking them off it!) and see how it fits.
Or further still, knit until you think it's OK and if after working the Crown it isn't long enough, rip out those few rows and add in some extra length. We are only dealing with a few rows in each stripe after all, and that gives us the freedom to custom knit.
And of course if you're going for the wonky square top then you'll want to knit all your length into the Body!