Is there a rule of thumb for this?

I am working a baby blanket with Bernat Softee Baby … the label says to knit on a size 6. I am going to double the yarn to make a slightly thicker fabric. I knit a swatch on size 10 and size 9 and feel like the size 10 needle makes the fabric a little too loose for a baby so I am started on the 9’s…now I am having second thoughts.

Is there a rule of thumb on how to guage what size needles to use when doubling yarn ?

No, there’s no set rule. What you did is what is suggested–try different needles until you get the fabric you want.

You did just right! :thumbsup: