Hello. Can I substitute 8/4 cotton for 5/2 (mercerized)? Would I need to adjust the sett?

Many thanks.

This article from the JST Knowledge Base might help - https://janestaffordtextiles.com/knowledge-base/what-do-the-numbers-in-yarn-sizes-mean/

Thanks Sandra that is very interesting. So using this formula you can get the yardage per pound of cotton in this instance. the longer the yarn the thinner the yarn. For each pound.