What Is a Dimension? The Difference from a Metric and How to Use It in GA4

Once you start using GA4's reports and explorations, the words "dimension" and "metric" are sure to come up. While they are confusing until you get used to them, correctly understanding the difference between the two becomes the foundation for reading reports and reaching the data you want to know. This article clearly explains what a dimension is, how it differs from a metric, and concrete ways to use it in GA4.

What Is a Dimension?

A dimension is, in a word, the "angle" or "axis of analysis" for classifying data. It refers to the items for slicing numbers such as the number of users or page views by the angle you want to see, such as "by page," "by device," or "by region."

For example, with only the data "the site's total page views were 10,000," you can't tell which page is popular. By dividing the data with the dimension "by page," you can see the page views for each page. Analysis means dividing finely to examine, and a dimension plays exactly that role of "dividing" for that purpose.

GA4 has more than 150 dimensions available by default, letting you classify data by various angles such as page title and URL, the user's country, region, age, and gender, and the device used.

The Difference Between a Dimension and a Metric

Appearing often as a set with a dimension is the "metric." The two are easily confused, but they can be organized simply by considering their roles separately.

• Dimension: The angle / axis of analysis of data. Text items that basically cannot be expressed in numbers, such as "page," "device," and "region."
• Metric: The numbers that are the target of analysis. Values that can be counted, summed, or averaged, such as "number of users," "number of sessions," "number of page views," and "number of conversions."

The relationship of the two becomes clear at a glance when applied to the form "see △△ by ○○." What goes in ○○ is the dimension, and what goes in △△ is the metric. For example, in "see page views by page," "page" is the dimension and "page views" is the metric.

When in doubt, it becomes easier to judge by considering whether you can say "per ○○" or "by ○○," and whether a sum or average has meaning. The number of sessions has meaning as a sum so it's a metric, while the sum of male and female has no meaning so it's a dimension.

How to Use Dimensions in GA4

Dimensions can be used in both GA4's standard reports and exploration reports. Let's look at the basic operations of each.

Switching Dimensions in Standard Reports

Standard reports are convenient when you want to quickly grasp an overview of the data. For example, in the "Traffic acquisition" report, clicking the pull-down of the dimension name on the left of the table lets you switch to "Session source/medium," "Session campaign," and so on. This lets you check the same metric by different angles.

Combining Dimensions in Exploration Reports

When you want to analyze more freely, use exploration reports. The steps are as follows.

1. Open GA4's "Explore" and select "Free form"
2. Click the "+" of "Dimensions" on the left, add the dimension you want to use (e.g., Page title), and import it
3. Similarly, add a metric (e.g., Views) from the "+" of "Metrics"
4. Drag and drop dimensions to rows or columns and metrics to values to assemble the table

Since you can create a table just by dragging and dropping, flexible analysis is possible even without specialized knowledge.

Combining Multiple Dimensions

Dimensions can be used not just one at a time but in combination. For example, combining "gender" and "age" reveals a more concrete user image such as "how many male users in their 20s." In standard reports you can add a second angle as a "secondary dimension," and in explorations you can dig in from multiple angles in pivot-table form.

Angles Not Provided Are "Custom Dimensions"

When the dimensions provided in advance in GA4 are not enough, you can create a "custom dimension" to add your own angle. It is useful when you want to analyze data by your company's own classification not in the standard, such as "registered user / unregistered user."

Custom dimensions are created based on the values of event parameters sent from the site or app. Note that parameters you set on your own will not appear in reports unless registered as custom dimensions in the GA4 admin screen.

Examples of Easily Mistaken Dimensions

GA4 also has dimensions whose actual meaning differs from the impression their name gives. Let's keep the typical ones in mind.

• Default channel group: An item easily confused with "Session default channel group." In many analyses it's common to use "Session ~," and choosing the wrong one can make traffic appear low.
• Page referrer URL: Refers to the page viewed one step before, and is recorded regardless of whether inside or outside the site. Note that it does not represent only the external traffic source.

Rather than judging by the impression of the name alone, checking what each dimension actually represents before using it improves the accuracy of your analysis.

Conclusion

A dimension is the angle / axis of analysis for classifying data, referring to text items such as "page," "device," and "region." A metric, on the other hand, is a number such as "number of users" or "page views." Remembering that the ○○ in "see △△ by ○○" is the dimension and △△ is the metric makes it easier to organize. In GA4 you can use dimensions through switching in standard reports and combining in exploration reports, and using custom dimensions lets you analyze by your own angles too. Start by using familiar dimensions, and grasp the feel of reading data from multiple angles.