Webserver capability question

Hello all,

I have a question regarding my new webserver, i now we can’t calculate what a webserver can handle, but i want to calculate an estimate, the websites that are running on this server are mainly information websites or demo’s for upcoming items.

Server specs:
6 Intel Xeon CPU E5-2620 V3 @ 2.40 GHz [cache size 15MiB]
40 GB Memory
800 GB SSD
1 Gbits Unmetered connection

Server is running Linux Centos 7 with Plesk 12 Webhost.

How can i calculate how many websites i can host on this server based on these spec’s, just information websites. I know it depends on allot, but just an estimate.