In Google Analytics, dimensions are characteristics of the user that visited your site and include things like: browser & version, operating system, campaign, channel, screen resolution, and many, many more. (Visit the Google reference on dimensions for a complete list.) While Google Analytics has over 125 (more if you use AdWords and / or Ecommerce) dimensions already baked-in and set for you; users of the free platform can add their own – up to 20.