If you want to measure the characteristic of a user that cannot be measured by any default dimension, then you need to create and use your own dimension to measure such characteristics.
In the context of GA4, a custom dimension is an event parameter. This parameter can be an automatically collected parameter, custom parameter or user property.
Do not send personally identifiable information (like name, email address, house address, phone number, social security number, etc) to your GA4 reporting view as a value of the custom dimension. This is against the Google Analytics terms of service.
Following are the various subcategories of custom dimensions:
Event-scoped custom dimensions
User-scoped custom dimensions
Event-scoped custom dimensions
A custom dimension whose value is calculated and sent for each event is called an event-scoped custom dimension.
We create an event-scoped custom dimension by registering a parameter with event scope in the GA4 user interface.
A custom dimension whose value is calculated and sent once for each user is called a user-scoped custom dimension (aka a user property). We create a user-scoped custom dimension by registering a parameter with user scope in the GA4 user interface.
The following are the two main advantages of creating and using custom dimensions in GA4:
#1 In your event report, you see a new data card added for every logged event parameter you registered as a custom dimension.
This data card appears in every event report where you (or GA4) are passing the same event parameter along with the event. Thus the use of custom dimensions enriches your existing event reports.
#2 You can report on the same event parameter for as many events as you like (via add comparison and Analysis Hub reports) without passing the same parameter over and over again for each individual event.
In Universal Analytics, a custom dimension can have anyone of the following four scopes:
Hit
Session
User
Product
Whereas in GA4, a custom dimension can have only one of the following two scopes:
Event
User
Note: In GA4 the ‘hit’ scope is referred to as ‘event’ scope.
#2 Different processes for creating custom dimensions
In Universal Analytics, creating a custom dimension involves the following two steps:
Configuring (setting name and scope) the custom dimension in the user interface.
Writing a code to send the values of the custom dimension to the reporting view.
In GA4, creating a custom dimension involves the following two steps:
Sending an event parameter along with an event.
Registering the logged event parameter as a custom dimension in the user interface.
#3 Different quotas for custom dimensions
In Universal Analytics, you can create up to 20 custom dimensions per property. However, if you are using the GA 360 then you can create up to 200 custom dimensions per property.
Whereas in GA4, you can create up to 50 event-scoped custom dimensions and 25 user-scoped dimensions per GA4 property.
How to edit a custom dimension
Follow the steps below to edit a custom dimension:
Step-1: Navigate to the Custom Definitions report in your GA4 reporting view:
Step-2: Click on the three dots menu next to the custom dimension you want to edit:
Step-3: Click on the ‘Edit’ option:
Step-4: You can now change the name of your custom dimension and/or edit its description. Then click on the save button:
Quota information for custom dimensions
In GA4, you can create up to 25 user-scoped custom dimensions and up to 50 event-scoped custom dimensions per property. That’s the dimensions quota allocated to you.
Now if you want to know the total number of user-scoped and event-scoped custom dimensions you have already created and the number of dimensions you are still allowed to create then you can get this information through the ‘Quota information’ feature of GA4.
Follow the steps below to find the quota information:
Step-1: Navigate to the Custom Definitions report in your GA4 reporting view:
Step-2: Click on the ‘Quota information’ button on the top right-hand side of your screen:
You should now be able to see the total number of user-scoped and event-scoped custom dimensions you have already created and the number of dimensions you are still allowed to create:
How to delete a custom dimension
In GA4, you can create up to 25 user-scoped custom dimensions and up to 50 event-scoped custom dimensions per property.
However, once you have reached your custom dimensions quota, you can then no longer create any new custom dimension. In that case, if you still want to create new custom dimensions, then you would need to delete the ones you are no longer using.
Follow the steps below to delete a custom dimension:
Step-1: Navigate to the Custom Definitions report in your GA4 reporting view:
Step-2: Click on the three dots menu next to the custom dimension you want to delete:
Step-3: Click on the ‘Archive‘ option:
Step-4: Click on the ‘Archive’ button:
Note: Archiving a custom dimension is permanent. It can not be undone and the corresponding data can not be restored. Any segment or funnel using this custom dimension in Analysis would stop working.
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