Category Archives: Techniques

The Maths of Knitting a Circle

This post is a response to Episode 130 of the Knit Knit Café, a knitting podcast of which I have become a regular listener.

‘Guest Barista’ Susan is trying to work out the maths of knitting a flat-topped hat, where the top is circular. Listen to the podcast section from 31:30 onwards and you can hear the original discussion, where Abby and Susan between them describe the problem much better than I can! But basically the question is this – what is the decrease formula for working out how to knit a flat circle from the outside in?

It’s just maths, of course*. I am a relatively new knitter and I have never actually tried this, but I am very mathematically inclined and I see no reason why the following wouldn’t work. Bear in mind that we are knitting in the round here, so each ’round’ is actually part of a long spiral.

Before you start you need three numbers:

  • S = the number of stitches that you are starting with around the outside edge of your circle (the circumference)
  • C = the length in inches of your circumference
  • G = your row gauge – that is, how many rows you knit for a vertical inch of knitting.

Step 1 is to calculate r = the radius of your eventual circle.

r = C ÷ 2 ÷ pi


Step 2 is to times r by G, your row gauge. So let’s say you’ve worked our your radius to be 3 inches and your row gauge is 6 rows/inch, then you do 3 x 6 = 18 . The number that you end up with is the number of rounds that you need to work to get to the middle of your circle – let’s call is N.

Step 3 is to take S, the number of stitches around the outside of your circle, and to take away 3. Call this number D. D is the number of stitches that you need to decrease in total in order to end up with 3 stitches left at the middle of the hat.

So we now have the following: (if you are nervous of doing algebra then I suggest that you write these out in a separate list with the calculated number next to each letter so that you have an easy reference)

  • S = the number of stitches that you are starting with around the outside edge of your circle (the circumference)
  • C = the length in inches of your circumference
  • G = your row gauge – that is, how many rows you knit for a vertical inch of knitting.
  • r = the radius of your circle
  • N = the number of rounds that you’re going to need to work, and
  • D = the total number of decrease stitches

Step 4 (nearly there!): do D ÷ N. This will tell you how many stitches you need to decrease on each round, using your favourite decrease. In order to get a nice even circle, you should try and spread the decreases out around the circle as much as possible, and try not to decrease at the same point on next-door rounds.

At the end of this, you’ll end up with 3 stitches left. Break the yarn, and pull the tail through the stitches to secure them.

One important thing to note is that you will very rarely end up with nice whole numbers to work with, so you may have to do a bit of ‘fudging’ to end up with something sensible – it’s obviously not possible to decrease exactly 5.4 stitches per round, for example! Just bear in mind that you want to keep everything as symmetrical and even as possible in order to get a nice smooth circular shape. This will be easier in lighter weight yarns where a single stitch corresponds to a smaller measurement in inches.

If anyone tries these instructions, by the way, I’d love to hear about it and to see your results!


*This is one of the things that I love about knitting, incidentally – so much is “just maths”! Geek, me?


Block Fusing

I have had a day off today, courtesy of being able to use my annual leave allowance whenever the hell I like, and the sewing mojo has struck. The shimmery fabric that I bought at Abakhan’s at Easter has been begging to become a summer dress, and who am I to refuse such pleas when the sun is finally shining and I have a wedding to go to next month?

This fabric is beautiful. It washed on 30 degrees and dried practically before it was out of the machine. It’s a gorgeous colour and a gorgeous drape… but a pig to cut out because the grain is practically non-existant and it’s unstable as heck. Not great for the fitted bodice that I’d be envisaging.

But then I realised that I had a solution! I could underline it. Better still, I could effectively underline it with interfacing before cutting, thus preserving the shape of the pieces, stabilising, and de-wrinkling all in one go. I use ‘proper’ interfacing from Gill Arnold. Essentially it’s a fabric in its own right – it has a warp and a weft, and means that the fabric you apply it to remains its drape. It’s not cheap, but the difference between it and the stiff, papery stuff that you buy for 30p/metre from the Rag Market… well there’s just no competition. They’re pretty much different notions altogether.

In classic block fusing, you fuse a whole area of interfacing to a whole wrong side of fabric and then lay your pieces out as normal. In order to preserve as much of my precious cotton fusible as possible, I simply cut out my pattern pieces from the interfacing, fused them onto the spread-out fabric and then cut around the fused shapes.

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This will make the everything much easier to sew as well as cut, and because the exposed side of the interfacing feels like a smooth cotton, I reckon I’ll get away without having to line anything either. Win!

A Word On Yarn Overs

This post is mostly aimed at new(er) knitters (than I). I have no intention of teaching my grandmother to suck eggs.

When I was first looking at the instructions for JSSBO, it took me a while for me to wrap my head around it. I kept repeating her knit stitch instruction to myself: “wrap the [yarn the] opposite direction around the needle from the standard yarnover”.


And then when I was looking for information on yarn-overs in another context (more on which another time), it suddenly clicked into place. There are two different types of yarn-over.

Let’s go back to what a yarn-over is trying to achieve. See this diagram of stockinette (cribbed from Ignore what the needles are doing. The bits I’ve filled in in blue are a small continuous section of yarn as it came off the ball. You can see that there is a short horizontal bar between the loops of yarn that form stitches over the needle. The idea of a yarn-over is to create a new stitch out of that bar by lifting it over the needle itself, in between the current stitches.


One way to achieve this is to do what I have always done, which is to just bring the yarn between the two needles to the ‘opposite’ side of the work when you reach the place that you want the new stitch. So, bring the yarn through the needles to the front if the next stitch is a knit stitch or bring the yarn through the needles to the back if the next stitch is a purl stitch. If you’re switching between knitting and purling on the same row, then you may just be able to leave the yarn on the opposite side of the work.

This works because when you come to knit (or purl) the next stitch, the yarn has to find its way back to the correct side of the work, so it travels over the needle as you are forming the stitch.

You’ll appreciate that when using this method, Jeny’s instruction doesn’t make much sense.

So what I found is that there’s another technique called a ‘yarn-over’. Instead of letting the yarn travel back over the needle itself, you actively take it there: bring the yarn forward through the needles, but then loop it back over the needle before forming your knit stitch. On the purl side, it would seem that you perform the wrap first (taking your yarn over the needle to the back) but then bring it forward through the needles.

Either method has the same result: forming a new stitch from that horizontal bar. But the method where you actively wrap the yarn over means that you have a looser tension on the next stitch because the knitting doesn’t have to ‘correct’ itself, I presume resulting in a slightly bigger hole.

Clever, eh? I would imagine that one’s considered American and one British or something. It certainly makes sense of the distinction between ‘yarn over’ and ‘yarn forward’. The method that I’ve been using seems to have worked fine for me so far and I’ve no particular intention of fixing what’s not broken – but I do like being able to understand my knitting like this, and understand why certain techniques produce certain results.

WIP Detail Shot #3

Maybe “knitting in macro” should have it’s own category. I do love how my camera has picked up the subtleties in the charcoal cashmere.

IMG_6319 (600 x 450)

Of course, an alternative name for that category could be “knitting mistakes in macro”. Less sexy, somehow.

I didn’t think of it originally but taking such a clear photo and ‘annotating’ it in Paint really helped me see what was going on amongst that tiny (4 ply), dark yarn.


FO: Knitted Baby Dress

I finished the baby dress/tunic, first shown here.

IMG_6254 (450 x 600)Cute, no?

There isn’t a lot to say about this dress, really, but a couple of notes. The pattern is ‘Button Tunic’, which has a fold up pocket all around the hem secured with buttons. As incredibly sweet as this feature is, I was knitting the one year old size, and buttons near babies are to be treated with caution. Plus, this was an instant gratification project, people! I didn’t want to be futzing around with buttonholes and what have you.

I did take inspiration from the colour-blocking of the original, and knitted the dress as a canvas for this funky multicoloured acrylic (I presume) that I have had in my posession for yeeeears. The cream stripes at the bottom are knit in garter stitch – partly as a design feature, but partly to lend some weight and anti-curling support to the lense dense multicoloured stockinette. There is a single garter row on each sleeve hem, too, as an echo.

As I knitted the dress in the round, I used techknitter’s tutorial for jogless stripes. The result isn’t perfect, but it’s a lot better than obvious spirals would have been! I don’t suppose that anyone will be looking anyway.IMG_6257 (450 x 600)

Another ‘first’ knitting-wise is that this is my first garment knit top-down, with yoke and sleeves as one piece. It will definitely not be my last – it was so satisfying once I’d worked out what was going on! Actually a pattern lingering near to the top of my queue on Ravelry is constructed in the same way, so watch this space…

Now I just have to find a suitably cute recipient. All bar one of the babies that I know of the appropriate age are boys – and the one girl has an elder sister who would also need a knitted present to make it fair. I am not pregnant (nor do I have any wish to be in the immediate future!) and I can’t help feeling that putting the dress into the Bottom Drawer will only provoke Sod’s Law into giving me boys in the years to come. Still, enough of my friends seem to be sprogging that I’m sure the Buttonless Tunic will find a home soon enough 🙂

WIP: My First (Knitted) Armscye Seam

IMG_6242 (450 x 600)

It’s a bit of a lumpy one, especially around the top of the sleeve cap. Hopefully it’ll look a bit better with steaming and blocking. I did have a more detailed shot which Jonathan took for me, but I, um, deleted it off the memory card by mistake.

I’ve been doing whipstitch. Mattress stitch is clearly the recommended technique for unobtrusive seaming, but seems to assume that you’re joining two vertical pieces together (which clearly I am not).

Do the more experienced knitters out there have any advice?


Between writing and publishing this post, I did a bit of searching on Ravelry, which lead me to this Knitty article: mattress stitch for sleeves. So I think I’m going to be unpicking, blocking the whole thing, and trying again.

(I’m a little terrified of the blocking too, by the way. My gauge swatch suggests that all horizontal measurements will grow by an eighth – hence the rather close fit at present. But what if it doesn’t work out and all my hard fitting work is ruined?)

It’s frustrating because I want to wear it NOW. The snow is falling thick and fast outside and I desperately need more work appropriate jumpers. But I know that I will wear the result a lot more if I actually get it right. Patience, girl, patience.