I use KnitPick's formula to find the perfect hat size everytime :D
1. Measure the circumference of the person's head you're making the hat for. [example: I'm 21"] This is measurement A.
2. Pick out what needles and what yarn you want to use to knit the hat with. Make a swatch with these needles and yarn, in stockinette if you plan to do the hat in the round and/or do stockinette on the hat -- maybe like 15 stitches by like 5-10 rows? Just to get a really good swatch size to sample from. Count how many stockinette stitches it takes to reach 1" of knitting. [example: let's say with the particular yarn and needles I'm using it's 4 stockinette stitches = 1"] This is measurement B.
3. Multiply measurement A x measurement B. [example: 21 x 4 = 84] now round down (because it's always better to make a hat that fits a little snug rather than too big) to a number that is divisible by 8. [example: 80] This is measurement C.
4. Cast on measurement C! [example: I would cast on 80 stitches]
5. For a plain hat (like in my avatar) I do k2, p2 ribbing for 2 inches. Then I switch to stockinette stitches (since I work in the round, it's just plain knit stitches) until the hat is as tall as I want it to be. I am constantly trying it on my head, so try it on your 9 year old's head often! Once it's tall enough, I start decreasing. Here's how the decreases go:
1. Once the hat is tall enough, on the start of the next row/round, knit 8 stitches, then place a marker. Knit 8 more stitches, then place a marker. Repeat this, placing a marker every 8 stitches, until you're back to the beginning. [example: now you know why we chose to cast on a number that was divisible by 8; it makes the decreases easier]
2. This is technically the first actual decrease row/round. Start knitting along until you are 2 stitches before a marker. Knit those 2 together. Then keep going normally until you are once again 2 stitches from the next marker, then knit those 2 together. Keep the markers as you go. Just keep knitting around, always knitting the last two stitches before the next marker around and around and around until you're down to too few stitches left on your needles (if you're working in the round on fixed circular needles) and switch to DPNs or magic loop if you're not already.
With the decreasing to finish the hat you can either keep going, decreasing with the 2 stitches before a marker continuously until you're out of stitches or you can stop when you feel you're down to only a couple left (if you're working on circulars you'll know when this is because it suddenly gets too uncomfortable to continue) and then cut a long tail, run it through the last few loops you have and pull tight to cinch it closed. Keep in mind if you choose to end it "drawstring-style" like that, it will take some of your height so the hat may end up a little shorter than you wanted. (Ask me how I know, lol)
I know this was a really long-winded reply, but hopefully it'll help. I know I struggled a lot getting hats (one of my absolute favorite things to knit) to fit properly and this "formula" that I saw outlined in a KnitPicks video on YouTube suddenly made it all click and was like magic. Hope it works for you! Good luck <3
ETA: LOL what suzeeq said!
Last edited by pinktoque : 05-08-2009 at 02:28 PM.
Reason: haha what suzeeq said!