Event-scope means the value of the dimension is calculated and sent for each event. 

GA4 Event-scoped dimensions provide insights into the context surrounding a specific user event (e.g., purchase, video play). They capture details specific to user actions (events) on your website or app.

For example:

• Product category for a purchase event
• Video title for a video play event
• Button text for a click event. etc

Event-scoped dimensions apply only to the event they are associated with, not to the entire session.

There are two categories of GA4 event-scoped dimensions:

#1 GA4 Built-in event-scoped dimensions – These are ready-to-use dimensions available in the GA4 reporting interface or data API.

#2 GA4 custom event-scoped dimensions – These are user-defined event-scoped dimensions.

GA4 Built-in event-scoped dimensions

The following table provides a brief description of the various GA4 Built-in event-scoped dimensions:

GA4 custom event-scoped dimensions

The custom event-scoped dimensions are user-defined dimensions.

If a built-in event-scoped dimension does not capture the detail relevant to your business, create its corresponding custom event-scoped dimension.

Let’s say you run an e-commerce website and want to track clicks on a “Subscribe” button to understand how often users engage with this call to action. 

GA4 does not have a built-in event-scoped dimension specifically for tracking “Subscribe” button clicks. 

Therefore, you need to create a custom event-scoped dimension to capture this detail.

How to identify event-scoped dimensions in GA4?

GA4 Event-scoped dimensions do not have a prefix (like ‘source/medium’).

That’s how you know they are event-scoped:

Note: The source and medium for non-key events in GA4 are “(not set)”.

GA4 Event-scoped dimensions vs Attribution.

For event-scoped dimensions, by default, GA4 assigns conversion credit using data driven attribution model.

Event-scoped dimensions are affected by changes to the reporting attribution model (you select under Data Display > Attribution Settings):

However, it is important to clarify that event-scoped dimensions themselves do not use the reporting attribution model.

This is because the values of event-scoped dimensions do not change based on user behaviour or the attribution model you choose.

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Consider the following user journey:

#1 Clicks a Facebook ad: The user clicks a social media ad on Facebook, directing them to your website. This interaction is captured by the session-scoped dimension “Session Source/Medium” with the value “facebook / referral.”

#2 Browses “clothing” category: While browsing the website, the user specifically interacts with the “clothing” category. This detail is captured by the event-scoped custom dimension “product_category” with the value set to “clothing” for the specific event of browsing that category.

#3 Signs up for newsletter: The user completes a key event by signing up for your newsletter.

The value “clothing” remains constant, reflecting the product category the user browsed, regardless of the user’s prior actions or the attribution model chosen.

Even though the user arrived through a Facebook ad, the attribution model you’ve selected (e.g., last click, data-driven) determines how credit for the newsletter signup (key event) is ultimately assigned.