Almost every pattern says something like "be sure to check your gauge." But what is gauge, how do you check it and what does it mean for your projects?
What is Knitting Gauge?
Gauge is simply a measurement of the number of stitches and rows per inch of knitting. Many yarn labels will say something like "US 9 needle, 3.5 stitches per inch" or show a graphical illustration of a grid with numbers around the outside and a drawing of needles with a number beside them.
For instance you might see a grid with a 31 on the side, a 22 on the bottom, and an 8 next to the needles. It also says 4 inches at the top. This gives you a lot of information about the yarn. It tells you that the "average knitter" using size 8 needles will get 22 stitches and 31 rows across over four inches of knitting, usually garter stitch.
Likewise, most patterns will give you a measurement of gauge, such as 10 sts (a common abbreviation for stitches) and 16 rows equals four inches. That means that four inches of knitting in the pattern stitch would give you 16 rows and 10 stitches.
Why Gauge is Important
So if you know the gauge used in your pattern and the gauge listed on your yarn are the same, why can't you just knit your project with confidence?
The answer goes back to the idea of the "average knitter." In reality, there is no average knitter. Everyone knits a little differently; some people knit loosely, while some knit very tight (it shouldn't surprise you that gauge is also referred to as tension). When you give the same yarn and the same sized needles to two different knitters, the odds are very good that they will come up with a different gauge, and they might both be different than the gauge listed on the yarn label.
It's important to check your gauge before you start a project and see how your knitting compares to the gauge of your pattern.
Why Check Gauge?
If your number of stitches and rows per inch doesn't match the pattern you are working with, the size of your finished product will be different from the pattern. For some projects like scarves this might not matter very much, but for something fitted like a sweater it can make a big difference.
Let's say for example that the pattern has a gauge of 10 stitches per inch and you're getting 11 stitches instead. It doesn't sound like a big difference, but doing a little math can show you what a difference a stitch can make.
Let's say your finished project is supposed to be 30 inches wide. In the pattern's gauge, that means you'd have 300 stitches. But if you divide those 300 stitches by 11 stitches per inch instead of 10, your width is only going to be a little over 27 inches, meaning your sweater won't fit.
Many knitters hate to check their gauge. They think that knitting a gauge swatch is a waste of time. But knitting a sweater that's way too small is a waste of time, too.