If I hold two strands of a DK weight yarn together, does it equal a worsted weight?
No; 2 strands of DK would equal bulky. 2 of sport would equal worsted.
:think: I think there is a link about this, but I’m not sure where it is. Anyway, I suspect it would be heavier than that.
I hate to go against the tide, but I have used two strands of DK to substitute for worsted weight and it worked. What you should do (and yes I know a lot of knitters like to avoid this step) is to knit a gauge swatch (wash and block it) to see if holding two strands of that particular DK yarn you’re considering works with the pattern you would like to make.