How to tell if I need more memory / have excessive paging

I'm taking some time to see what my typical usage looks like as I plan out my PC build, and trying to decide between 16 and 32GB of RAM. I'm watching Performance Monitor for % Usage and % Usage Peak for my current 16GB laptop but want to make sure I'm interpreting correctly - at what percentages should I start thinking about 32? Is there something else I should be looking at?