How do I know when traffic is too high for droplet based on graphs?

How do I read the graphs? What’s too high CPU usage, memory or disk IO? As an example, I have various basic droplets, all 1 CPU, 1GB ram, and Ubuntu 20.04. I run a few websites on each of them, Grav CMS on Nginx, very lightweight flat-file cms. All the websites have very low traffic, I have an average CPU usage of less than 1% and a few spikes to 10% every few days, while the ram is about 30% all the time, I guess that’s just for running the OS. How do I know when these numbers are too high and it’s time to create a new droplet for new sites? I used to create a new droplet for each site, but after I learned how to properly setup Nginx blocks I started putting multiple sites on the same droplet and didn’t see any drop in performance. Disk IO is usually around a few kb/s with random peaks lower than 2MB/s, same goes for bandwidth.