Does anyone know how yarn weight changes when you double strand together to substitute yarn in a pattern? Example, what would I weight would I get if I double stranded sock weight together or dk weight or worsted weight, etc?
I think, since yarns can vary a little, even in the same weight, the only way to know for sure would be to knit a swatch with the two strands, then measure. But I could be wrong; I’m still pretty new to knitting myself. Maybe the more advanced knitters can give you a better answer. 
I’ve used two strands of worsted weight to substitute for bulky weight. Here’sa chart.
Gee, thanks for the Standardization link. It is a great site
OTN: socks, mittens, and soon to be my first big project: a sweater for me.