How to Measure Knit Gauge
Gauge is the number of stitches and rows per inch (or centimeter) in a pattern. If the gauge does not match the gauge given in a pattern, the item you're making will not end up the correct size.
A gauge swatch is a small sample of your pattern that you make before starting the main item. It allows you to measure the gauge, so you can make sure that you will not run out of yarn and the finished item will be the size you want it to be. Not matching gauge isn't as important for something like a dishcloth or a bag, but for garments and accessories the wrong gauge could mean the finished item is too small to put on or fit for a giant.
How to Knit a Gauge Swatch
When knitting a gauge swatch, always work with the same yarn you're using for the main item. Cast on enough stitches for your swatch to be 5-6 inches [12.5-15.25 cm] across, and knit enough rows to make a square. Work in the same pattern that the gauge calls for. If different gauges are given for different stitch patterns, make sure you make a swatch for each stitch pattern. If no pattern is given for the gauge, work in whatever the main stitch for the item is. If the pattern calls for multiple sizes of needles, use the size mentioned in the gauge.
Sometimes the gauge is given in pattern repeats. For example, for a ripple pattern, the gauge may say that from one point to another point of the ripple is 5" [12.5 cm].
For patterns made of individual pieces, the gauge might be given as the size of a finished piece. For example, a throw made of squares might give the gauge as the finished size of a square.
Other times, instead of a gauge, there may just be a note that the gauge is not important for the project. If you're making a Scrubby dishcloth for example, it doesn't matter if the finished item is exactly the correct size, or uses slightly more of the ball of Scrubby.
How to Measure a Gauge Swatch
After completing your gauge swatch, place it on a flat, hard surface with good lighting. Use a ruler or gauge measuring device to count the number of rows and stitches in the number of inches given in the pattern gauge. The best practice is to count over 4", but some gauges call for 2" or 1", especially if the yarn is very thin. The gauge swatch should be larger than the area you need to measure, so you can just use the interior stitches to measure your gauge. Remember, half-stitches count too!
What if my gauge doesn’t match the pattern gauge?
Unless you knit with the exact same tension as the designer, your gauge won’t exactly match up with the pattern gauge using the same yarn and hook or needle size. This is normal! To make your gauge match, choose a different needle size.
If you have more stitches and rows per inch than the pattern calls for, use a larger size needle.
If you have fewer stitches and rows per inch than the pattern calls for, use a smaller size needle.
For this sweater, the gauge is 21 sts= 4" [10 cm] and 28 rows = 4" [10 cm] in Stockinette stitch. Consider size Medium, which has a finished bust measurement of 40". If you have 19 stitches in 4" [10 cm], instead of the 21 called for by the pattern, you will end up with a finished sweater with a bust measurement of 44" — much too big! Conversely, if you have 23 stitches in 4" [10 cm], you will have a finished sweater measuring 36 1/2" — way too tight.
Uses for Gauge Swatch
Treat your gauge swatch the way you would treat your finished item: block it and wash it to make sure you know how to take care of your work when it is complete. You may find that it wants to stretch some when washed, for example, and you must carefully lay it flat to dry.
When you’ve finished your item and don’t need the gauge swatch anymore, recycle it! Combine it with other swatches to make pillows, bags, afghans....whatever you can envision! Make sure you only use it in projects with similar yarns, so the care instructions will be the same throughout all parts of the project.