How to Knit a Swatch & Calculate Gauge
Swatching and calculating gauge is ESSENTIAL to make sure your garment fits! Swatching is also a great way to test yarns to make sure they will produce a fabric suitable for the garment, and to practice pattern stitches used in the pattern.
Make a swatch that is at least 6” square, including the border. THIS IS NOT A WASTE OF TIME OR YARN!
Most patterns use stockinette stitch for gauge measurements, but if your pattern uses a different stitch make your swatch in the stitch specified in the pattern.
The pattern should specify how many stitches you should have in 4″. If it only specifies the stitches per inch, multiply that number by 4 to get the number of stitches in 4″.
You will get an much more accurate measurement over 4″ than over a smaller space. This is critical since a 1/4 stitch difference in your gauge can result in a garment that doesn’t fit, and it’s difficult to recognize a small difference like that if you are only measuring 1″.
It’s a good idea to cast on at least 12 stitches more than the number of stitches called for in the pattern gauge. Six stitches will be in the border and you want extra stitches in the measuring area so your measurements aren’t skewed by the border stitches. The garter stitch border will have a different gauge than the stockinette center, and the size of stitches close to the border can be stretched or scrunched by the border.
This example is for a stockinette swatch with a garter stitch border. The garter stitch border keeps the swatch from curling.
Knit Your Swatch
Cast on the number of stitches specified in the pattern gauge plus 12, using the cast on specified in the pattern. If it does not specify a particular cast on, use whatever cast on you prefer.
Rows 1-6: Knit
Row 7: K3, purl to last 3 sts, k3
Row 8: Knit
Repeat rows 7 & 8 until your swatch is at least 5”
Last 6 rows: Knit
Bind off with the bind off used in the pattern or whatever bind off you prefer.
I like to “record” my needle size by putting eyelets in my swatch. So for a size 7 needle, I would put 7 eyelets in it by doing (yo, k2tog) 7 times in row 8.
If you are using a 1/2 size needle (1.5, 2.5, or 10.5), you can add an eyelet in row 10 to indicate the 1/2.
If you’d rather record the mm size, use the same technique putting eyelets in row 8 for the whole numbers, and eyelets in row 10 for the fractional bits. For the fractions, I’d use 1 eyelet for each 1/4mm.
Measure Your Gauge
When you finish knitting your swatch, measure the number of stitches in 4” in the center of the swatch. Tip: insert darning needles in your swatch at 0″ and 4″. Then count the number of stitches in between the needles. That way, you don’t have to hold the tape measure while you count.
Repeat this process for measuring the rows. Write down your stitch and row counts, but don’t use these for your gauge. You might need these numbers later.
Wash and block your swatch. After it is dry, measure the number of stitches and rows in 4” in the center of the swatch again. These are the numbers you want to match to the pattern gauge.
If you have more stitches in 4″ in your swatch than what the pattern calls for, it means your stitches are smaller than the pattern gauge. Do another swatch with a larger needle.
If you have fewer stitches in 4″ in your swatch than what the pattern calls for, it means your stitches are larger than the pattern gauge. Do another swatch with a smaller needle.
Sometimes it’s hard to match both the row gauge and stitch gauge. It’s usually best to match the stitch gauge, as many patterns are easy to adjust by knitting more or fewer rows if the row gauge doesn’t match.
I recommend that you fasten the yarn label to your swatch, note the size and type of needle you used, and store all your swatches in one place. When you record all this information, you can refer back to it for future projects and you will never have to swatch with that yarn and needle size again – assuming you don’t change the type of needle you use or your knitting technique.
However, don’t assume that all yarns of a particular wieght will have the same gauge. For example, if you have 26 stitches in 4″ for one fingering weight yarn, you will not necessarily have the same gauge with another fingering weight yarn.
The fiber content, the way the yarn is spun, and other factors can affect gauge. One common example is that superwash yarn always “grows” more with blocking than untreated wool yarn, so if 2 yarns were exactly the same in every aspect except one was superwashed and the other wasn’t, they would have different gauges because of the superwashing.
Accounting for Blocking Growth
Many patterns instruct you to knit for x number of inches, or they have diagrams depicting the finished measurements. Those measurement are usually post-blocking. (Pattern authors have no way of knowing what yarns knitters will choose, so they cannot write patterns to accomodate blocking growth.)
This is where your pre-blocking measurements come in handy. You can use those numbers to figure out how to adjust your knitting to accomodate for how much your garment will grow when you block it.
FAIR WARNING: Swatches lie! Or so I’ve been told. Before I give you a math lesson, I want to point out that this only works if you block your garment in the same manner as you blocked your swatch.
If you decide you want your final garment to be wider and you block it more aggressively to widen it, you will consequently shorten it.
When you want your garment to be longer and you block it more aggressively to lengthen it, it will be narrower.
If you blocked your swatch with even aggressiveness on the length and width but stretched your garment as described above, the gauge on your garment will not match the gauge on your swatch. You blocked them differently.
Changing the shape in blocking is OK, but don’t depend on it to work miracles (like increase your garment 2 sizes).
OK. Back to calculating blocking growth. The formula is:
# inches to knit = # rows in post-blocking gauge / # rows in pre-blocking gauge * measurement stated in pattern
Let’s say a pattern tells you to continue knitting for 17″. And your gauge is:
- 28 stitches and 38 rows in 4″ pre-blocking
- 26 stitches and 36 rows in 4″ post-blocking
To figure out how many inches you should knit so that this section of your garment will be 17″ after blocking, the formula is:
36 rows / 38 rows * 17″ = 16.1″
So, you will knit 16.1″ of stockinette stitch, and after you block it, it will grow to 17″.
The good news is that it’s not worth the effort to calculate this for small spans. So the only time you’ll need this formula is for large measurements.
And if you’re really math-averse and don’t want to do this, I encourage you to guesstimate how much shorter to knit your piece.
Customize Your Garment
Knowing how to make simple adjustments to your patterns allows you to customize any pattern to fit you perfectly. Learning how to adjust the overall size of a garment is the first step to customizing a pattern. Click here to learn how.