How much RAM does a Minecraft server need for how many players?

I just wanted to ask how much RAM a Minecraft server (1.15.2) needs for how many players. I know that this is also related to the CPU & plugins, but a rough estimate should be possible. By the way, I only use PremissionsEx for plugins and a plugin that virtually controls the entire server, even programs it myself. How much RAM do I need now e.g. For 100 players?

If you still want to use plugins etc., I would recommend 5 / 6Gb Ram for 100 players. Then it should also run very smoothly

Thank you for the quick & compact answer!
Can you actually calculate it down so proportionally, e.g. For 20 players 1GB RAM or something else?

As in your case, it should already be 8-10 Gb

So just as an example. I offer server hosts over the Internet. If you book a server for 100 players with me, I always add 6Gb RAM so that everything runs as smoothly as possible. I think 1 / 2Gb should be enough for 20 players.

1 GB per 20 players

Depending on the size of the world 1 to 2 GB (if each player loads a different part of the world, it takes much more than if ten players load the same area)

For plugins / mods 1-2 GB extra, depending on how many.

= 6-9 GB.