Matomo (Piwik) lets you measure several websites within one Matomo server. Each website added into Matomo has its very own ID Site (or Website ID).

To find out the idSite value for a given website, you can follow these steps:

  1. Log into your Matomo.
  2. Go to Administration (click on the gear icon in the top right of the screen).
  3. Click on the Measurables(or Websites) > Manage page. You will find a list of all websites on this page.
  4. The website ID is on the left of the table listing all websites directly below the website name.

If you are using Matomo for WordPress, your Site ID should be 1 and you can double check this ID in Matomo Analytics > System Report > Matomo Blog idSite.