This post is to answer a question one of the knitter's asked me: "How do you adjust this pattern for an adult?"
Please, see below my solution how I would do it. If anyone has a different solution, I am sure we all would be happy to read another comment-suggestion below this post or on G+.
This hat was casted on (CO) 60 sts, and it measures 15" and stretches up to 19" (which, actually, would be very tight around the head should anyone with 19" circumference wear it). Therefore these sts and inches tell us that there are 4 sts per inch. If adult head is 21" in diameter then that is 6" extra from original measurements. However it may be a little too lose to wear it. So maybe for regular wear you would like your hat-scarf to measure 20" instead, and for a windy environment (such as driving in convertible) you would probably want it tighter - therefore 19" would be probably better.
So for each extra stitch you would add 4 sts and for each BO in the back you would need to bind of extra 2 sts - provided that you are knitting with cotton of #4 (worsted) thickness.
13" circumference = CO 52 sts, BO in back 11 sts
14" circumference = CO 56 sts, BO in back 13 sts
15" circumference = CO 60 sts, BO in back 15 sts => original pattern from my video
16" circumference = CO 64 sts, BO in back 17 sts
17" circumference = CO 68 sts, BO in back 19 sts
18" circumference = CO 72 sts, BO in back 21 sts
19" circumference = CO 76 sts, BO in back 23 sts
20" circumference = CO 80 sts, BO in back 25 sts
21" circumference = CO 84 sts, BO in back 27 sts
and so on...
With the decrease toward the tip, you would just decrease as many times as you would need to (just like in the video) until your last 3 sts.