The key to accurately measuring gauge is to work your swatch in the same way that you plan to work the knitted piece. Translation: if you’re knitting a sweater in the round, your swatch should be knit in the round, too.
Why swatching in the round matters
You'll use the right stitches
When knitting stockinette flat, you purl on the wrong side — for many knitters, those purl stitches are a little looser than their knit counterparts (hey, we're not robots!). By contrast, when knitting stockinette in the round, you work only knit stitches. So, it follows that if you're knitting a sweater of all knit stitches in the round, you need to knit your swatch the same way. And this isn't a special stockinette only situation — it's best practices to always knit your swatch the same way you'll knit your sweater. Before you roll your eyes and knock out another flat swatch for your in-the-round sweater, introduce yourself to the "speed swatch."
Making a “speed swatch”
The speed-swatching technique described below allows you to make a larger swatch with a handy shortcut, so that knitting a swatch in the round doesn't have to be frustrating and time consuming. So grab your circular needle (any length is fine), and get started!
How to knit a speed swatch step by step
Cast on as you regularly would. Make sure your swatch will be at least 4"-6" wide and the same in height. The bigger you can make it, the more accurate it will read.
Then, slide the cast-on stitches across to the other end of the needle. The working yarn should now be closer to the cord of the circular needle.
Holding the working yarn loosely around the back, begin knitting onto the free needle.
Work all the way across.
When you get to the end of the row, slide the stitches back to the other needle. Remembering to keep the working yarn loose across the back of your work, begin knitting again across the row.
Repeat Steps 2 and 3 until you are done with your swatch. Bind off as usual.
Here’s what your swatch will look like from the back:
A few quick tips for speed swatching in the round
If you find that the yarn floats in the back are too tight and are tugging on your knitting, simply cut them, like we did on this blue swatch. They won’t unravel, and you’ll get a more accurate read.
As you knit, if you think your gauge might be off, switch to a different needle halfway through, like we did on the swatch above. That way, you can wash and dry one swatch and easily compare the gauges.
Don’t forget, if you plan to block your finished piece, you’ll want to block this swatch as well. Lay it as flat as you can,with the floats on the bottom. From there, simply measure your stitches and rows as described here.