How to Set Custom Dimensions and Metrics in Google Analytics 4
Custom definitions (also known as custom dimensions and metrics) are critical to any business that relies on Google Analytics, and they have been completely overhauled in Google Analytics 4. In this post we will discuss how custom definitions have changed and review the steps to set them up correctly.
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This post has been updated to show the benefits of upgrading to New GA 360.
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Updating to include item-scoped dimensions now that they are fully available
What Are Custom Dimensions and Metrics?
If you are familiar with custom definitions in Universal Analytics then feel free to skip this section. Otherwise, here is a quick definition:
Any time you fire a hit to Google Analytics, a variety of data points are collected automatically so that they can be used for analysis later. A few examples include:
- A description of the content that is currently being viewed (such as the URL or app activity)
- A unique identifier for the user (such as the client ID or device ID)
- Information about the device being used (browser, screen resolution, etc)
Custom definitions were introduced with Universal Analytics in 2013, and they allow you to add other data points to the hit that are custom to your website or application. These data points are called custom dimensions and custom metrics (they are equivalent to eVars and success events in Adobe Analytics).
When creating custom dimensions in Universal Analytics, you also determine if the scope should be set to “hit”, “session”, “user”, or “product”. This is important, because your selection here determines the types of reports you can build (more on that here).
| Hit | Describe the current hit | Ex. Page title |
| Session | Describe the entire session If more than one value is set during the session, the later values will overwrite the previously set values. |
Ex. Login status |
| User | Describe the user If more than one value is set, the later values will overwrite the previously set values. |
Ex. Account status |
| Product | Describe the product If more than one value is set, the later values will overwrite the previously set values. |
Ex. Color |
How Custom Dimensions have Changed in Google Analytics 4
The new version of Google Analytics still allows you to create custom definitions (and custom metrics remain relatively unchanged), but you cannot create dimensions with a session scope any longer. The scope of your custom dimensions will now be set to either the hit level (now called event scope), user level, or the product level (now called item scope).
This means that a custom dimension should always describe the event itself, the user who triggered the event, or the product that is being interacted with.
If you previously set custom dimensions that describe your sessions in Universal Analytics or some other Analytics tool, you will need to be a bit strategic about how to pass those attributes into Google Analytics 4.
Which brings us to our next topic…
How to Migrate Custom Dimensions to Google Analytics 4 from Universal Analytics
To reiterate the section above, it is no longer possible to set the scope of a custom dimension to the session. Although the concept of a session still exists in GA4, it is far less important than it was in Universal Analytics (more about that here).
In many cases you can set what was previously a session-scoped dimension as a hit-scoped dimension. If this will not work for you, BigQuery receives a random number that is used to identify each session called "ga_session_id", and you can use this to aggregate a dimension by session if you have enabled the BigQuery integration.
How to Properly Configure Custom Dimensions in Google Analytics 4
In GA4, custom dimensions and metrics are created from your event parameters, so to set a custom dimension or metric, you simply provide it with a name, and identify the parameter that should populate it. It is okay if the parameter is being set by more than one event, because all events with the identified parameter will feed the new dimension/metric.
The example below will generate a new custom dimension called “foo” using the “Google Analytics: GA4 Event” tag in Google Tag Manager:
Event parameter in GTM
About 24 hours after data has started collecting to this parameter, you can navigate to the "Custom definitions" report in Google Analytics, and create a new custom dimension or metric. The new parameter ("foo") will show up in the "Event parameter" drop down similar to the "file_extension" parameter that is shown in the screenshot above.
Once you've set the parameter as a custom metric or dimension, two things will happen:
- A new data card will be added to the report for this event.
Data card
- The new dimension/metric will be available for use in your Exploration reports.
New dimension
Limits
In Universal Analytics, properties running the free version were limited to 20 custom dimensions and 20 custom metrics. When you upgraded to GA360, your quota was extended to 200 custom dimensions and 200 custom metrics.
With Google Analytics 4, you can create 100 hit-scoped custom dimensions or metrics (50 of each: source), 25 user-scoped and 10 item-scoped (source). If you upgrade to the enterprise version (called "New GA 360") then you will be able to create 250 custom dimensions or metrics, 100 user-scoped, and 25 product-scoped.
How to Remove Unused Custom Definitions
If you no longer need a custom dimension or metric, you should remove it so that it does not count towards your limit. To do this, you can go to your "Custom Definitions" screen, and "Archive" the dimension or metric that you would like to remove (read more here).
Archive a custom definition
| WARNING |
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| Once a custom dimension or metric has been archived it cannot be recovered. Any audiences or reports that rely on this variable will not work. |
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Add a comment in the community if you have issues or additional questions related to custom definitions. I will expand this article over time to share more best practices as I come across them.
