Alternative yarn weight and needle size

I am a beginner. I have a pattern using worsted weight yarn (9wpi 10 ply) using size 9 (5.5) needles. I want to knit this is dk (double knitting) wool. What size needles should I use please?

Welcome to the forum!
It all depends on the gauge you get with your yarn and needles. You can start with a needle size around 5-7US but it’ll depend on the yarn and your tension. Once you’ve knit a swatch you’ll be able to see if you like the knit fabric too.
If you substitute DK for worsted without changing the pattern or size, you’ll knit a smaller sweater. The easiest thing to do it to work a larger size if there is one in the pattern. You might also look for a similar pattern written for DK.

Thank you. I am only knitting a cowl and really wanted to use the double knitting wool. I will maybe just experiment!

I would personally use a us 7 or 8 needle, but a swatch would definitely help you decide.

Thank you I will try. :+1: