To find out the total number of registered users on your Matomo (Piwik), first log in to your Matomo as a Super User. If your user has the Matomo “Admin” role then you might not see all the users.

In Matomo 3 and newer

When you are logged in, click on the “Administration” icon in the top right corner to load the admin area.

The number of users is shown in the widget “System Summary” in the top left of the administration home page.

In Matomo 2

When you are logged in, click on the “Administration” icon in the top right corner to load the admin area.

Click on “Users” in the left menu of the administration area, then scroll down to the “Users Management” section. It will show you the total number of users registered on your Matomo in the first paragraph of that section.