Gauge, also known as "tension", is very important to knitters, however new knitters seemed to be confused by it and experienced knitters often skip this step when starting a new knitting project with much regret later when they have to frog, undue all their knitting.
Gauge is the expected number of stitches within a certain amount of knitting. It is usually expressed in stitches and rows in yarn patterns and on yarn labels. But sometime the gauge will only have the number of stitches. In the United States the number of stitches and rows are usually written for 1 or 4 inches.
The gauge in a pattern tells you how many stitches and rows you must have using the recommend knitting needle.
You should always make a gauge swatch before starting a project. Usually, this is a 4-inch piece of fabric.
Cast on the number of stitches called for in the pattern and then knit in the recommended stitch pattern. Many times this is stockinette but could also be the pattern’s particular stitch pattern.
After knitting the recommended rows, bind off and measure the piece’s width and height. If it is 4 inches then you have the proper gauge. If it is to wide and tall then undo the knitting and try again with a smaller sized knitting needle. If it is not wide or tall enough then undo the knitting and try again with larger sized knitting. You will continue to this until you get the proper number of stitches and rows.
Using a knit gauge measuring ruler makes checking gauge easier. Often these rulers come with a needle size checker as well.
If you don’t do a gauge swatch and check that your are knitting in the gauge the pattern recommends then your item may be too large or too small. This can be disappointing and a lot of wasted time and effort.