Dimensions and metrics
Understand the building blocks of your reports.
Every report in Google Analytics is made up of dimensions and metrics.
Dimensions describe characteristics of your users, their sessions and actions. The dimension City describes a characteristic of sessions and indicates the city, for example, "Paris" or "New York", from which each session originated. The dimension Page describes a characteristic of page view actions and indicates the URL of each page that was viewed.
Metrics are quantitative measurements. The metric Sessions is the total number of sessions. The metric Pages/Session is the average number of pages viewed per session.
The tables in most Google Analytics reports organize dimension values into rows, and metrics into columns. For example, this table shows one dimension (City) and two metrics (Sessions and Pages/Session).
Valid dimension-metric combinations
Not every metric can be combined with every dimension. Each dimension and metric has a scope: users, sessions, or actions. In most cases, it only makes sense to combine dimensions and metrics that share the same scope. For example, Sessions is a session-based metric so it can only be used with session-level dimensions like Source or City. It would not be logical to combine Sessions with an action-level (or, hit-level) dimension like Page.
For a list of the valid dimension-metric pairs, use the Dimensions and Metrics Reference on the Developer site.