In digital marketing measurement, measuring basic page views only shows you that a user landed on a page — it doesn't show you how much of the content they actually read. If visitors leave your site after scrolling only 10% of the page, your content is failing to engage them. Implementing a custom **GA4 scroll tracking configuration** using Google Tag Manager (GTM) is the most reliable way to monitor user engagement levels and optimize copy layouts.
How GA4 Tracks Scrolls by Default
GA4's Enhanced Measurement includes a default scroll event. However, this default event only fires when a user reaches the exact 90% threshold of the page height. It does not track intermediate steps (like 25%, 50%, or 75% scroll depths), leaving you blind to exactly where users lose interest and drop off.
Step-by-Step GTM Scroll Tracking Configuration
Step 1: Create the Scroll Depth Trigger in GTM
- Log into Google Tag Manager, go to Triggers, and click New.
- Select **Scroll Depths** as your trigger type.
- Check **Vertical Scroll Depths** and enter percentages: 25, 50, 75, 90.
- Set the trigger to fire on all pages or configure it to run only on your "/blog/*" subdirectories. Name the trigger **Trigger - Vertical Scroll depths**.
Step 2: Create a New GA4 Event Tag
- Go to Tags → New in GTM. Select **Google Analytics: GA4 Event** as the type.
- Select your measurement configuration. Set the Event Name to scroll_depth.
- Under Event Parameters, add:
- Parameter Name: scroll_depth_percent | Value: Select the GTM variable {{Scroll Depth Threshold}}.
- Parameter Name: page_path | Value: Select {{Page Path}}.
- Add the Scroll Depth trigger to this tag. Save and publish.
Step 3: Register Custom Dimensions in GA4
To view your scroll depth metrics in GA4 reports, register the custom parameter as a custom dimension:
- Log into GA4, navigate to Admin → **Custom Definitions**.
- Click Create Custom Dimension. Name it "Scroll Depth Percent".
- Set the Scope to Event and set the Event Parameter to scroll_depth_percent. Save.
Standard Engagement Parameters Matrix
| GA4 Event Name | Custom Parameter | GTM Variable | Reporting Purpose |
|---|---|---|---|
| scroll_depth | scroll_depth_percent | {{Scroll Depth Threshold}} | Tracks user vertical scroll depths (25%, 50%, 75%, 90%). |
| page_view | page_referrer | {{Referrer}} | Identifies where users came from. |
| click | link_url | {{Click URL}} | Tracks outbound links clicked by users. |
| user_engagement | engagement_time_msec | N/A (GA4 Auto-tracked) | Measures active tab session time in milliseconds. |
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