How I do a Tenion (Gauge) Swatch

I started a new project recently. It's a pair of socks for my best friend from primary school. The first Christmas after I learned to knit, I made her a red lace scarf, the next year a red lace beanie, the next year red lace gloves, so this year for Christmas I'm making her red lace socks. Because I wanted to get the sizing right, I did a proper tension/gauge swatch, and I thought I'd share how I test my tension, and discuss a couple of other methods I've tried. To aid your understanding, please enjoy my very high quality MS Paint diagrams.

What is Tension/Gauge?
Tension (called "gauge" in the USA, and maybe Canada) refers to the amount of stitches and rows you can knit in a given area, on a given weight of yarn with a given needle size and stitch. For example, consider and 8 ply acrylic yarn, knit in stocking (stockinette) stitch on 4mm needles. Your average knitter will knit about 22 stitches and 28 rows in a 10cm X 10cm (4in X 4in) square. Of course, averages are statistical calculations, so don't necessarily represent any real person's tension. And as hand-knitters, our tension may well change day to day, row to row, or even stitch to stitch (hopefully it's not too uneven though). This is why it's important to check your tension.

I don't always check my tension before starting a project, but I do believe that they're important if you're going to do something where accurate sizing is important.

Tension for Knitting Patterns
At the start of knitting patterns, the designer will almost always include a section for tension or gauge. These things usually look something like this:

Tension: 34 sts/48 rows = 10cm X 10cm in stocking stitch

Tension guides on knitting patterns usually quote expected numbers for a 10cm square, but sometimes will quote for a 1 inch (2.5cm) square. Similarly, tension guides usually give you expected tension for stocking stitch. However, some patterns, especially those with featured stitch patterns, like lace, will give you tension for that stitch pattern.

So, What is a Tension Swatch, then?
A tension swatch is a square that you knit in the recommended needle size and the yarn you are planning to use, to see if your knitting produces the same tension as those recommended. If you find that your swatch has more stitches and rows per 10cm square, your finished object will turn out too small. You'll need to go up a needle size and knit another swatch to see if those needles are better. Conversely, if your swatch has fewer stitches and rows per square, your finished object will turn out too big, and you'll need to go for a smaller needle size.

Great. So how do you do a tension swatch?

The Method I use: 15cm X 15cm (6in X 6in) Square

When I first learned to knit, I borrowed this book from my local library. It contained information for how to do a tension swatch. I've tried other methods, but I still turn to the method described in this book for my "Gold standard" of tension. So this is how I do it.

  1. Plan a 15cm X 15cm swatch (not 10cm). Why? You're not bound to get an accurate count of your stitches and rows since edge stitches often curl round the edges, and I don't know if it's just me, but my selvedge stitch are looser than the others. Also, if your tension turns out to be tighter than that given by the pattern, your square will be smaller than 10cm squared and you won't know how far off you are.

    To calculate what is a 15cm square, multiply the stitches and rows from the pattern's tension guide by 1.5. So, if your pattern says that 20sts X 30 rows makes 10cm squared, you would cast on 30sts and work in stocking stitch for 45 rows. If your tension is dead on the guide, your square will be a 15cm square.
  2. Once you have done this swatch, it will be curly, as stocking stitch is. Since you're bothering to do a tension swatch, you're probably planning on bothering to block or steam your finished project. Therefore, you need to block or steam your swatch. You might also want to beat up the swatch a little too, to imitate everyday wear and tear, since knitted objects may stretch over time. I will usually block swatches properly, washing briefly in warm water and laundry liquid, then rinsing in warm water. However for this pattern, I couldn't be bothered going to those lengths, so instead I thoroughly washed the swatch in warm water and squeezed it out. See my diagram for how I did it: 

 After you've wet your swatch, you need to pin it out to dry. Pin it out square, but don't stretch or compress it so that it fits into a 15cm square. That defeats the purpose of the swatch. I would normally use sewing pins, the ones with the colourful heads, but I don't have any in Tasmania, sew (pun intended) I used sewing needles. I could never have done this in Adelaide. My female dog Bubbles loves metal things. Once, my mum noticed that Bubbles would yelp every time she got into her bed. Turns out she had been collecting the sewing needles I would inadvertently drop when I wove in ends etc. (I had a tin full of sewing and darning needles) Thank God she never ate any of them (she has eaten other sharp metal things before). I now keep much better track of my notions. Anyway, I digress. Here is what it looked like when I pinned out my swatch:
Once it is dry, grab your ruler or tape measure and count the number of stitches (including half stitches) and rows in a 10cm square. As I said before, if you have a greater number of stitches/rows than the tension guide, your finished object will be smaller than the design. Fewer stitches/rows than the guide, it will be larger than the design. If you're one or two stitches off, you might not want to bother adjusting the needles size and re-swatching. If you want, you can calculate, based on your own tension, how big your finished object will be, and then decide if the finished size will do the job.

Other Ways to Swatch
I save my tension swatches and am planning to turn them into a  blanket when I have enough. I have some half-arsed ones that I might also put in the blanket, I haven't decided yet.

That's all. Here's a picture of a beetle: