Thanks to the gauge swatch, you get to know your yarn and the selected pattern - and above all: your own knitting. The right stitch gauge helps you to achieve the desired measurements with the given amount of yarn.
Why is the stitch gauge so important?
Knitting is handiwork. That means that everyone knits a little differently. With their own individual yarn tension. Some knit a little more loosely, others a little more tightly. It's the same with handwriting, which produces its own unique typeface. If I write larger letters, I need more space. If I knit loosely, the fabric becomes larger. In order to actually achieve the desired size with the specified amount of yarn, you need a guideline, a scale. These are the stitch gauge specifications. They show us the designer's handwriting, so to speak, and we imitate it. We can't change our style in the long run. But conveniently, we can achieve smaller stitches with smaller needles. And vice versa.
What do I have to keep in mind?
The swatch is a small preview of your finished knitted piece. Therefore, it must not only be made in the same way but also needs to be treated the same way after knitting it. If you are supposed to knit a certain stitch pattern according to the instructions and wash and block the garment at the end, this also applies to the swatch. Only then is it really meaningful.
How do I make the gauge swatch?
If the instructions for the gauge say, for example
24 sts x 34 rnds = 10 x 10 cm (4 x 4 in) over St St with 3.5 mm (US 4) needles after blocking
you should make a 10 x 10 cm square with the respective yarn and with 24 stitches over 34 rows in stockinette stitch. The suggested needle size is 3.5 mm (US 4). To make the knitted square easier to handle afterwards, you should definitely make it larger. Above all, this will give you a much more authentic picture of your personal knitting style. So cast on at least 10 more stitches and knit at least 10 more rows. The bigger you make it, the better you get into your personal knitting flow. To prevent the edges from curling up later on, you can also add a small border in garter stitch to your sample.
Wash and block the finished swatch in the same way as you would your knitted piece. Wet-blocking is the process of spreading the knitted piece smoothly on a flat surface, giving it the desired shape and allowing it to dry. Shawls with lace patterns in particular need a little tension so that the pattern and the shape can fully unfold. There are helpful tools for this, such as special blocking mats and pins.
When your swatch is completely dry, pick it up and shake it out a little so that the stitches can relax. Then lay it down flat again and count how many stitches you have knitted in exactly 10 cm (4 in) width and how many rows in 10 cm (4 in) height. It's best to use a ruler because measuring tapes can wear out over time. There are also special gauge rulers for this purpose.
Now compare your result with the information in the pattern:
Does your gauge swatch have fewer stitches than indicated in the pattern?
-> Knit again with a smaller needle size.
Do you have more stitches?
-> Try again with larger needles.
Repeat this process until the number of stitches matches the number given in the pattern. This is the right needle size for you. If your row count differs, you can try needles made of different materials (wood, bamboo, aluminium, carbon...). A rougher or smoother surface will give you more or less friction and change the tension of your thread.
Now you can really get started with the needle size that suits you best. And in the end, you will be rewarded with a well-fitting garment. With every gauge swatch you make, you get to know and assess your personal knitting handwriting better. Soon you'll be able to achieve the right size effortlessly.
And if you want to be absolutely sure when buying...
... that you will get by with the amount of wool, just order one skein more if in doubt. That way, you'll have enough yarn in the same dye lot, and you can knit without worry. If you have any unopened skeins leftover, you can return them here without any problem.