Other people answered how it’s measured, but if you’re just shopping for a CPU I’d recommend skipping straight to benchmarks. There’s a lot of technical stuff involved but if you look at Geekbench/Passmark scores you can easily compare which ones are more powerful.
If you’re shopping for a laptop with a specific CPU I’d also look into how much power it uses (in Watts).
I’m personally using https://alexandrite.app/ , which you can use regardless of which instance you’re on.