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What Is a Dimension in Google Analytics?

A dimension in Google Analytics is an attribute or characteristic of your data — a way of describing what happened, not counting it. Country, Device Category, Page Path, and Session Source are all dimensions. They pair with metrics (the numbers, like Sessions or Event Count) to build every report: a table of "Page Path" (dimension) next to "Views" (metric) is how you see which pages get traffic.

Dimensions vs. metrics

Every GA4 report is built from two kinds of columns: dimensions and metrics. A dimension describes something — it's a category or attribute, like Country, Browser, Page Title, Event Name, or Session Source. A metric counts something — it's a number, like Sessions, event count, Conversions, or Engagement Rate.

Reports pair the two together. Take the "Landing page" dimension, add the "Sessions" and "Key events" metrics, and you get a table showing which landing pages bring in traffic and which of those visits convert. Change the dimension to "Session source / medium" with the same metrics, and you get the same numbers sliced by where traffic came from instead. The dimension controls how rows are grouped; the metric controls what gets counted in each row.

Standard dimensions GA4 collects automatically

GA4 captures a set of dimensions automatically for every hit, with no setup required: Country, City, Device Category, Browser, Operating System, Page Path, Page Title, and Session Source/Medium are all collected out of the box. These are what populate GA4's standard reports without you configuring anything.

Custom dimensions

A custom dimension is one you define yourself, tied to a parameter you send along with your events. A common example is "user_type" — sending free vs. paid as a parameter on relevant events, then registering it as a custom dimension in Admin > Custom definitions so it's available in reports and explorations.

GA4's free tier allows up to 50 event-scoped custom dimensions per property, plus a separate allowance for user-scoped ones. Scope matters: an event-scoped custom dimension attaches to the specific event it was sent with, while a user-scoped custom dimension attaches to the user and persists across their sessions. Picking the wrong scope is a common reason custom dimension data looks incomplete or inconsistent — see what cannot be collected by default for related limits on what any tracking setup, custom or not, is able to capture.

FAQ

What's the difference between a dimension and a metric in GA4?
A dimension is a descriptive attribute of your data, like Country or Page Path. A metric is a quantitative measurement, like Sessions or Event Count. Reports combine a dimension with one or more metrics to build a table or chart.
What are examples of standard GA4 dimensions?
Country, City, Device Category, Browser, Operating System, Page Path, Page Title, and Session Source/Medium are all automatically collected standard dimensions.
How many custom dimensions can I create in GA4?
The GA4 free tier allows up to 50 event-scoped custom dimensions per property, with a separate limit for user-scoped custom dimensions.
What does "scope" mean for a custom dimension?
Scope determines what a custom dimension attaches to. Event-scoped dimensions apply only to the specific event they were sent with; user-scoped dimensions attach to the user and carry across all of that user's sessions.

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