A couple of years ago, when I was relearning to knit, I also ventured my first few steps into knitting in the round.
One of the first projects I did knitting in the round was this super simple spiral hat, that can be found on the darn. knit. (anyway) blog.
I love this pattern for its simplicity. It’s as straightforward as it comes, but better than just boring old stockinette stitch. I love the way it turns it into a lovely spirally pattern. If you have some self striping yarn it’s even better.
The instructions on the blog are for a specific yarn and a baby size, but it’s very easy to adapt it to all head sizes.
Step one: measure the target head.
Step two: take your yarn and look at the label. It will give you an indication of how how many stitches go in 4 inches/10 cm. Cast on that many stitches plus half that number at least again. Knit an inch or two, cast off.
Step three: measure and see how many stitches you really have in 10 cm / 4 inches.
Step four: now, do a few simple calculations. Divide the the number of stitches determined in step three by 4. This is the number of stitches per inch (I use metric, but I know most of my readers are American and probably use imperial. If you prefer metric, divide your stitches by 10: this is the number of stitches per cm).
Next multiply the circumference of your target head by the number of stitches per inch (or cm) you just calculated. Round this number down to the nearest even number: this is important for this pattern that that relies on two stitches knit together each time!
Your target head belongs to a baby and is 40.5 cm / 16 inch around.
You knit a little swatch and determine you have 26 stitches per 10 cm / 4 inch.
This means 1 cm equals 2.6 stitches, or 1 inch equals 6.5 stitches.
You’ll have to cast on 40.5*2.6=105.3 (cm calculation) / 16*6.5=104 (inch calculation) stitches.
If you are knitting a hat as a surprise present, Woolly Wormhead has this excellent table of head sizes.
In case you’re wondering, the outcome isn’t exactly the same due to not completely accurate conversion between cm and inches here. As you’d need to round down the 105 stitches to 104 anyway to get an even number, you still get the same result. In general though, it is important to be aware of potential discrepancies due to converting from imperial to metric and back again. This is actually rarely a problem as most knitters stitch to one or the other anyway. That’s the crucial bit: pick one system of measurement for a project, and stick with it. Seriously. Space projects have failed due to conversion issues!