Xanathar’s Guide to Everything (affiliate link) introduces an alternate method for building and balancing encounters. It replaces the DMG’s version which involves a bunch of addition and multiplication with a new method that uses fractions. If you’re having flashbacks to learning math as a kid (or maybe you’re a kid and you’re learning fractions now, I don’t know), don’t worry. I’ve got you covered.
I have filled in some gaps in the tables to support handling higher/lower CRs than indicated in the official rules, and I can’t really explain how it all works without wandering into copyright infringement. Go grab a copy of Xanathar’s, read the Encounter Building section in chapter 2, then hit the encounter builder to help you with the math.