How to Measure Gauge in the Round
Measuring gauge in the round takes some care. Knitting stockinette stitch in the round can give you a different gauge measure than knitting the same stitch flat. You get a different gauge in the round because a purl stitch is very slightly larger than a knit stitch.
Furthermore, when you work stockinette stitch on straight needles, every other row is a purl row, and the difference in the sizes of your knits and purls averages out. However, when working stockinette stitch in the round, you always make knit stitches, which can result in a slightly smaller piece even though you’re knitting the same pattern over the same number of stitches.
When the gauge for a project worked on a circular needle must be exact, make your gauge swatch by working all the rows from the right side:
Using the same needle you plan to use in your project, cast on 24 stitches or so and work 1 row.
Don’t turn the work.
Cut the yarn and slide your knitting back to the knitting end of the needle.
Be sure you have the right side facing.
Knit another row and cut the yarn.
Continue knitting and cutting until you’ve completed your swatch, and then measure your gauge.
To measure gauge in circular patterns quickly and easily, do it while you knit the piece. Knit at least 1 1/2 inches in the round on the needles you plan to use, stop, and measure the stitch gauge and 1-inch of row gauge. This method is generally accurate enough for any kind of small project you’re likely to encounter at the beginning or intermediate level.