I have a pattern that calls for knitting with two strands of yarn. If I only want to use one strand of yarn, what changes do I need to take with the gauge of yarn and/or the needle size?
We need more information. What's the yarn and needle size used in the pattern? What do you want to change it to - just one strand of same the yarn as in the pattern or a thicker one that will be about the same as both together?
Agreed we need more info. And doing a gauge swatch with the yarn and needles you'd use would help, too.