There’s only a limited choice of GOTS-certified yarns on the market. Taking the yarn double increases the number of choices, but the label never mentions a needle size or a gauge for double yarn. I didn’t even start calculating, and I’m already feeling a headache coming up!
I wondered if there was some kind of simple rule, but Google couldn’t find it. Most probably that’s because I didn’t ask the right question, not because nobody ever wrote about it … Anyway, I set out to do my own tests and I started from the idea that doubling the yarn would require more or less 1,5 times the original needle size.
Bio Balance is a 3-ply yarn* composed of 55% organic wool and 45 % organic cotton. The label gives a gauge of 25 stitches by 35 rows for 10 by 10 cm with 3,5 mm needles. For a nice and regular fabric I knit Bio Balance with 3 mm needles. That results in a slightly different gauge: 26 stitches by 38 rows. Most probably on 3,5 mm needles the gauge would be as on the label but then the fabric would be a little bit loose to my taste.
When doubling the yarn I tried 4,5 mm needles and obtained a gauge of 19 stitches by 28 rows. That confirms the idea I had that doubling the yarn in general requires to multiply the needle size by 1,5.
But then I tried Semilla Melange …
Semilla Melange is a 2-ply yarn* composed of 100% organic wool. The label gives a gauge of 22 stitches by 28 rows for 10 by 10 cm with 4 mm needles. That’s surprising. With 4,5 mm needles I have a gauge of 25 stitches by 40 rows, with 5 mm needles I’m at 23 by 34. Larger needles wouldn’t make for a nice fabric. To get the gauge from the label with 4 mm needles I’d have to knit very loosely. When I knit the Murrayfield beanie I used 3 mm and 3,5 mm needles with Semilla Melange!
When doubling the yarn we had the nicest results with a 6 mm needle, resulting in a 16 by 26 gauge. That is quite far from multiplying the needle size by 1,5!
I’ve put all the figures together in a table. We’ll come back on this subject when we’ve tried other types of yarn and other needle sizes, because this is not enough to come to any kind of conclusion.
All samples were knit with white brass circulars from addi.
* n-ply is about the number of strands the yarn is made of, not the confusing yarn size indication