How to set up GA4 Custom Dimensions

It can be challenging to envision a complete setup of Google Analytics 4 without utilising custom dimensions or metrics. GA4 may not have all the predefined parameters required to collect specific information about our users, products, or actions. As a result, the use of GA4 custom dimensions and metrics becomes increasingly necessary. 

There are several instances where we may find ourselves in a situation where custom dimensions and metrics are essential. Let’s delve into their significance and explore how to utilise them in GA4.

What’s a custom dimension in GA4?

In the context of data analysis, dimensions are attributes that define and categorise your data. For example, in a campaign dataset, dimensions could include the campaign name and the campaign ID. 

In Google Analytics 4 (GA4), a custom dimension is a user-defined attribute you can add to your data to provide additional context. It is an event parameter you want to track that differs from the ones GA4 automatically tracks.

Overall, custom dimensions in GA4 provide the flexibility to track and analyse specific attributes unique to your business, enabling you to gain deeper insights and make data-driven decisions.

Benefits of using custom dimensions in GA4

The main benefit of custom dimensions is tailored tracking; this means you can configure GA4 to capture and track specific data points unique to your business. 

For example, for a content website, you can create a custom dimension to track user interests or preferences and use that to tailor content or recommendations to individual users. Another example would be a case where users need to fill out a form on your website, GA4 does not automatically collect this event. So, custom dimensions come in handy in this situation.

Tailored tracking offers benefits like advanced segmentation, granular reporting, improved personalization, and the opportunity to combine your GA4 data with your data from other sources, as you can track unique business data to give a comprehensive view of your users and their interactions with your business.

GA4 custom dimensions and metrics best practices

Custom definitions in GA4 refer to both custom dimensions and custom metrics. As previously mentioned, custom dimensions in GA4 are a form of custom definition that enables businesses to monitor qualitative attributes unavailable in default dimensions. Conversely, custom metrics are custom definitions that allow you to track and analyse specific numerical data points unavailable in the default metrics of GA4. 

It is essential to consider certain best practices when implementing them in GA4 to optimise the potential of custom dimensions or metrics.

Firstly, clearly define your goals and the specific data you wish to track. This will aid in identifying the most relevant dimensions and metrics for your business.

Also, when working with a standard property (i.e., the free GA4 version), avoiding creating high-cardinality custom dimensions or metrics is recommended. High-cardinality dimensions can adversely affect your reports, potentially causing data to aggregate under the “(other)” row. 

Although GA4 permits the creation of up to 50 custom dimensions and metrics, it is important to be selective and only create those that are genuinely essential. Given the limitation on the number of custom dimensions and metrics, it is advantageous to utilise recommended GA4 events instead of custom dimensions. 

Because most GA4 recommended events have event properties that are available by default in all GA4 reports (including GA4 Explore). Using GA4-recommended events and (or) their properties allows you to send business-related data through them without going above the GA4 custom dimensions limit. 

For instance, you can use the “method” event property for “sign_up” and “login” events or any other event. You don’t need to register “method” custom dimension in this case, it’s available by default.  

Additionally, it is crucial to establish a uniform naming convention and maintain comprehensive documentation that clearly defines the purpose, definition, and usage of each custom dimension. Here, we have provided a sample documentation you can use to achieve this.  This practice will promote consistency and understanding among team members. 

In the long run, regularly review your custom dimensions and metrics to ensure their continued relevance as your business needs evolve.

Difference between GA4 and UA custom definitions

There are several key differences between custom definitions in Google Analytics 4 (GA4) and Universal Analytics (UA). Some of them include:

  1. Scope/Type

Universal Analytics offered four custom dimensions: Hit, Session, User, and Product. While Google Analytics 4 offers three types of custom dimensions: User-scope, Event-scope, and Item-scope.

When you switch from UA to GA4, you should use the following rule to set up custom dimensions and metrics in GA4, as you cannot directly migrate them:

  • UA Hit Type -> GA4 Event -scoped type
  • UA User Type – > GA4 User-scoped type
  • UA Product Type – > GA4 Item-scoped type

While Google Analytics 4 does collect sessions, it primarily has an event-based measurement model. Consequently, collecting session-based custom dimensions may not be particularly meaningful; consider switching them to the event, user, or item-type custom dimensions for better alignment with GA4’s event-based measurement approach.

  1. Data processing

In Universal Analytics (UA), custom dimensions and metrics are processed during data collection, allowing them to be immediately available for reporting. However, in GA4, custom definitions undergo processing during data analysis, resulting in a delay of 48 hours before they become accessible for reporting.

It is crucial to consider these differences when implementing custom definitions in GA4, as they can impact how you track and analyse data in GA4.

How to set up custom definitions in GA4

To begin with, the process of configuring custom dimensions and metrics in Google Analytics 4 involves two steps:

  1. Registering the custom dimension or metrics in Google Analytics 4
  2. Configuring the GA4 event with the correct custom definition in Google Tag Manager

Both of these steps are crucial, and the order in which they are performed matters; if you set up it in GTM, publish container, you won’t be able to access the custom dimension data GA4 received within that time until it is registered in GA4. Once these steps are completed, it is important to note that the custom dimension data will become available 48 hours after implementation. It is worth mentioning that retrospective data cannot be viewed or accessed.

Now, let’s delve into each step in detail. I will show how to set up a custom dimension in GA4 using Google Tag Manager.

Register a custom definition in GA4 

Now, to register a custom definition go to GA4 -> Admin -> Custom definitions and create a dimension (or metric) in GA4.

Register a custom dimension
Register a custom dimension “percent_scrolled”

Provide the following:

  1. Dimension name. It can be any name that helps you to find this parameter easily.
  2. Select a scope. For my example, it’s an “event”.
  3. Description. Write a brief explanation to inform others what this parameter stands for.
  4. Select or write the parameter name you would like to use.
  5. Save the custom dimension (or metric).

Set up a custom definition in GTM

To set up a custom definition in GTM, create a new tag, select your Tag type, which is a GA4 Event, select the correct configuration tag, and then provide an event name.

Next, you need to create your parameters. For the event-scope custom dimension, you should use “Event Parameter,” and for the user-scope custom dimension, you should use “User Properties.”

Finally, set up the trigger. The screenshot below shows the event-cope custom dimension “percent_scrolled” I used to enable advanced scroll-depth tracking in GA4.

Scroll Depth as Event-scope Custom Dimension

After you have made all necessary GA4 tag adjustments in GTM, you should publish the GTM container, and then you can proceed to the following step.

Where to find custom dimensions and metrics data in GA4

After 48 hours, you can revisit Google Analytics 4 to view the initial data.

To view the data, follow the steps below

  1. Go to GA4 Explorations and create a new tabular report
  2. Import a new dimension to the report
  3. import “Event count” as a metric
  4. Add metrics and dimensions to the report
  5. Enjoy your data
GA4 Exploration Custom Dimension
GA4 Exploration Custom Dimension

You can also use your custom dimensions to build GA4 reports using GA4 Library functionality. 

What to do if you see (not set) for GA4 custom dimension?

Google Analytics 4 utilises “(not set)” as a default placeholder when information for a specific dimension is missing or not provided. This indicates that Google Analytics has not received the required data for that particular dimension.

In the first 48 hours, GA4 typically returns a value of “(not set)” for a custom dimension. If you encounter the value “(not set)” for a GA4 custom dimension after 48 hours, it indicates that you have not appropriately configured it.

To rectify the issue, take the following steps. First, ensure proper implementation of the custom dimension by verifying that it passes the appropriate parameters to GA4. Then, review the event mapping and conduct thorough testing and debugging using GA4 DebugView to identify any issues with the custom dimension implementation. Most importantly, refer to the GA4 documentation and utilise the troubleshooting resources provided by Google to address the specific problems related to custom dimensions.

GA4 custom dimensions in Google Looker Studio

You can leverage GA4 custom dimensions in Google Looker Studio to enhance your data analysis and reporting. Here’s how you can work with GA4 custom dimensions in Looker Studio:

  1. Connect GA4 data: Connect your GA4 data to Looker Studio by setting up a connection to your GA4 property. This will allow you to access and analyse your GA4 data within Looker Studio.
  1. Build reports and dashboards: Utilise Looker Studio’s intuitive interface to build customised reports and dashboards using GA4 custom dimensions, allowing you to gain deeper insights into user behaviour and engagement. Looker Studio automatically detects both the predefined dimensions provided by GA4 and any custom dimensions you have defined, enabling you to explore and incorporate them into your visualisations and dashboards. By incorporating GA4 custom dimensions, you can ensure that your reports and dashboards provide valuable insights into user behaviour and engagement.
  1. Create custom fields: In Looker Studio, you can create custom fields based on GA4 custom dimensions. These custom fields allow you to manipulate and transform the data from custom dimensions to suit your specific reporting needs.

By leveraging GA4 custom dimensions in Looker Studio, you unlock the full potential of your GA4 data by creating powerful visualisations and reports tailored to your business requirements.

How to delete or edit custom dimensions in GA4

How to delete or edit GA4 custom dimension or metric
How to delete or edit GA4 custom dimension or metric

If you discover that a custom dimension you have set up contains an error, there is no need to worry. In Google Analytics 4 (GA4), you can easily edit or delete a custom dimension. This provides you with the flexibility to correct any mistakes or make necessary adjustments to ensure accurate data collection and analysis.

To do that, go to GA4 -> Admin -> Custom definitions. Select the right dimension or metric and click on the three dots on the right side. Choose “edit” or “archive”. 

GA4 custom definitions limitations

Finally, let’s look at the limitations of custom dimensions in Google Analytics 4. 

Custom Definition Type

Standard property limits

Analytics 360 property limits

Event-scoped custom dimensions



User-scoped custom dimensions



Item-scoped custom dimensions



Custom metrics



Final Thought

In summary, custom dimensions in GA4 offer numerous benefits, including tailored tracking, granular reporting, advanced segmentation, and improved data accuracy. This helps you make more informed decisions, optimise your marketing efforts, and improve overall business performance.

Frequently Asked Questions

Does GA4 have custom dimensions?

In GA4, for a standard property, you can set up a maximum of 25 user-scoped custom dimensions, 50 event-scoped custom dimensions, and 10 item-scoped custom dimensions.

What is a custom dimension in Google Analytics 4?

A custom dimension is an event parameter that Google Analytics 4 (GA4) does not collect by default. You need modify your tracking code or use Google Tag Manager (GTM) to send the custom dimension data to GA4

What is a custom metric in Google Analytics 4?

The custom metric is an event parameter that Google Analytics 4 doesn’t collect by default. You need to modify your tracking code or use Google Tag Manager (GTM) to send it to GA4.

How do I add custom dimensions in Google Analytics 4?

To add custom dimensions in GA4, you should take the following steps:
#1 Register the custom dimension or metrics in Google Analytics 4
#2 Set up the GA4 event with the correct custom definition in Google Tag Manager

Does GA4 have calculated metrics?

Unfortunately, GA4 doesn’t support calculated metrics yet.

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