i need to know if, for example, the number of simultaneous customers submitting surveys is X the number of cores of CPU and memory should be xxx at least, and so on for other parameters.

How I can calculate this metric

This is not exact science. There is no formula for this, there are just too many variables, e.g.:

- length of the survey
- type of questions, equations, filters, etc.
- connection speed of the server to the internet (bandwith)
- connection speed of the respondents
- webserver configuration
- etc.

This might also change from LS version to LS version, some might need more resources, others less.

The best you will find are some real life experiences from users here in the forum. Have a search.

But even then: CPUs are not all the same, it also depends how you configured your server, the webserver, PHP, etc.