Both the mittens in the photo above were knitted by me, on double pointed needles (dpns), to the same pattern, in the same yarn, and for the same number of rows. However, the knitting at the top is on 5mm dpns; whereas the knitting beneath it is on 6mm dpns.
I clearly wasted time knitting on 5mm dpns. But for a small item, like these mittens, I don't usually swatch, for the simple reason that it's pretty quick to re-knit, if necessary. I also don't bother for blankets, scarves and the like, since fit is not such an issue.
It is however my usual practice to test for gauge for larger, fitted items, such as the apple strudel cardigan I finished recently. I test gauge by knitting a tension square - also called a swatch - before starting on the project proper.
Here are my tips for swatching:
Cast on and knit a square a bit bigger than required to test your tension, using the needles stated in the pattern. Most patterns state tension requirements for a square of 10 cms / 4 ins, so you'd need to knit a square of about 12 cms / 5 ins. It's important to use the right kind of needles, e.g. swatch on a circular needle for a project on circs, because the type of needle being used can influence your knitting style.
Measure and place a couple of straight pins to mark a 1o cms / 4 ins square on the swatch. Count the number of stitches (horizontally) and rows (vertically) in this square, then compare this with the stated gauge for the pattern.
- If there are too many stitches / rows, this means your stitches are too small. Try again with a slightly bigger needle
- If there are too few stitches / rows, this means your stitches are too big. Try again with a slightly smaller needle
If there are the right number of stitches / rows, your luck is in!
Actually, it's the number of stitches that is most critical. If there are the right number of stitches, but there are too many or too few rows, you may be able to address this simply by knitting more or fewer rows when following the pattern.
I hear the super-organised label up their completed tension squares, with a note of the yarn, needle type / size, and achieved gauge, so they can use the results for future patterns. Somehow I can't see that being immediately achievable for me, although I did sort out my yarn stash recently, so perhaps there is hope.