It is 20 points for all sites.
To find out how many points are required for any privilege, visit the sites' /privileges page. You can reach it from the dropdown next to your name in the top bar.
20 points is really low, I don't see any need to have that lowered any further. From the privilege page:
We can't allow anonymous participation on chat, so we require a small bit of parent site reputation to ensure that chat is reserved for active, engaged members of the community.