Substitute worsted yarn for dk

I have a poncho pattern that uses Nepal by DROPS Garnstudio Yarn (Group: C (16 - 19 stitches) / 10 ply / aran / worsted
Weight/yardage: 1.8 oz (50 g) = approx 82 yds (75 m)
Recommended needle size: US 8 / 5 mm
Gauge: 4" x 4" / 10 x 10 cm = 17 sts x 22 rows). I would like to use some yarn that I already have Rowan pure wool superwash dk (Fiber Content: 100% Superwash Wool
Weight: DK
Gauge: 5.5 sts = 1 on US 6
Weight/Yardage: 50g/137yds). Can I use dk instead of worsted weight yarn? If so, how do I adjust the stitch count?

You can try knitting a swatch with a couple of different needle sizes to see what the fabric looks and feels like then work out how many stitches by holding a ruler to your preferred swatch and counting how many sts. per inch you get then multiply that number by your chest size.
I don’t know if your pattern has shoulder shaping, or any other features with a stitch count that might need to be adjusted, but it should be do-able :slight_smile:

Could I use a double strand? Would 2 strands of the dk equal worsted?

2 strands of DK would be 16ply which is heavier than aran, closer to chunky/bulky weight.
Again, you can swatch with 2 strands to see what fabric you get and what stitch count per inch using a couple of different sizes of needles, but if there are any shaping features in your pattern you would need to adjust.
Have you looked here or on ravelry at the poncho patterns to see if there’s anything similar but using a dk weight?
This is a simple pattern search on rav for a free adult poncho in dk weight :
https://www.ravelry.com/patterns/search#query=poncho&availability=free&weight=dk&view=captioned_thumbs&sort=best&craft=knitting&fit=adult
There are a couple of Drops patterns you could use as a reference for stitch count etc. or you could change the weight to bulky and see what comes up :slight_smile: